PAUL  B.HOEBEft 

MEDICAL  BOOKS 

69E.59thSl.,N.Y. 


Columbia  Wini\)tv^itf\  ^ 
intl)eCitpofi5etD|9orfe 

COLLEGE  OF  PHYSICIANS 
AND   SURGEONS 


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http://www.archive.org/details/introductiontonOOherr 


AN  INTRODUCTION 


TO 


NEUROLOGY 


BY 

C.  JUDSON  HERRICK 

PROFESSOR  OF  NEUROLOGY  IN   THE  UNIVERSITY   OF   CHICAGO 


ILLUSTRATED 


PHILADELPHIA  AND  LONDON 

W.  B.  SAUNDERS  COMPANY 

1915 


Copyright,  igiS,  by  W.  B.  Saunders  Company 


PRINTED    IN    AMERICA 

PRESS    OF 

W.    Q-    SAUNDERS    COMPANY 

PHILADELPHIA 


PREFACE 


There  are  two  groups  of  functions  performed  b}^  the  nervous 
system  which  are  of  general  interest;  these  are,  first,  the  physio- 
logical adjustment  of  the  bodj'  as  a  whole  to  its  environment 
and  the  correlation  of  the  activities  of  its  organs  among  them- 
selves, and,  in  the  second  place,  the  so-called  higher  functions 
of  the  cerebral  cortex  related  to  the  conscious  life.  The  second 
of  these  groups  of  functions  cannot  be  studied  apart  from  the 
first,  for  the  entire  conscious  experience  depends  for  its  materials 
upon  the  content  of  sense,  that  is,  upon  the  sensory  data  received 
by  the  lower  brain  centers  and  transmitted  through  them  to  the 
cerebral  cortex.  Since  the  organization  of  these  lower  centers  is 
extreme^  complex,  and  since  even  the  simplest  nervous  proc- 
esses involve  the  interaction  and  cooperation  of  several  of  these 
mechanisms,  it  follows  that  an  understanding  of  the  workings 
of  any  part  of  the  nervous  system  requires  the  mastery  of  a  large 
amount  of  rather  intricate  anatomical  detail. 

Fortunately,  the  knowledge  of  the  precautions  which  must  be 
obser^^ed  in  order  to  maintain  the  nervous  system  in  health}'- 
working  order  is  not  difficult  of  acquisition  (though  surprisingly 
few  people  seem  to  have  gained  it),  just  as  any  one  can  learn  to 
operate  an  automobile,  even  though  quite  ignorant  of  the  engi- 
neering problems  involved  in  its  design  and  construction.  In- 
formation regarding  these  matters  of  practical  hygiene  is  readily 
available,^  and  it  is  not  the  primary  purpose  of  this  book  to  sup- 

^  GuLicK,  Luther  H.  1907.    The  Efficient  Life,  New  York. 

GuLiCK,  LuTHEK  H.  190S.    Mind  and  Work,  Xew  York. 

Jewett,  Fraxci.s  Gulick,  1S9S.  Control  of  Body  and  Mind,  New  York, 
Ginn  &  Co.     Adapted  for  use  in  the  <rraded  schools. 

LuGARo,  E.  1909.  ^Modern  Problems  in  Psychiatry,  ]Manchester 
Univer.sity  Press.  A  book  \\Titten  especially  for  physicians,  but  fuU  of 
stimulating  ideas  for  every  educated  reader. 

Stiles,  P.  G.  1914.  The  Nervous  System  and  Its  Conservation,  Phila- 
delphia, W.  B.  Saunders  Compan3^ 

11 


12  PREFACE 

ply  it.  But  to  understand  the  actual  inner  operation  of  the 
nervous  mechanisms  is  a  much  more  difficult  matter,  and  this 
knowledge  cannot  be  acquired  without  arduous  and  sustained 
study  of  the  peculiar  form  relations  of  the  nervous  organs  and 
their  complex  interconnections;  and  information  of  this  sort  is 
indispensable  for  a  grasp  of  the  principles  of  nervous  organiza- 
tion, and  especially  for  an  intelligent  treatment  of  nervous  dis- 
eases. 

The  study  of  neurology  is,  therefore,  intrinsically  difficult 
if  one  is  to  advance  beyond  its  most  superficial  phases;  the  more 
so  if  the  student  is  not  well  grounded  in  general  biology  and  at 
least  the  elements  of  the  general  anatomical  structure  of  the  ver- 
tebrate body.  To  these  inherent  difficulties  there  is  added  a 
purely  artificial  obstacle  in  the  form  of  a  cumbersome  and  con- 
fused terminology  which  has  grown  up  during  several  centuries  of 
anatomical  study  of  the  brain,  in  the  early  stages  of  which  little 
or  no  comprehension  of  the  functional  significance  of  the  parts 
discovered  was  possible,  and  fanciful  or  bizarre  names  were  given 
without  reference  to  the  mutual  relationship  of  parts. 

The  problems  which  at  present  chiefly  occupy  the  attention  of 
neurologists  are  of  two  sorts — first,  to  discover  the  regional 
localization  within  the  nervous  system  of  the  nerve-cells  and 
fibers  which  serve  particular  types  of  function  or,  briefly,  archi- 
tecture, and  second,  to  discover  the  chemical  or  other  changes 
which  take  place  during  the  process  of  nervous  function,  that  is, 
the  metabolism  of  the  nervous  tissues.  The  first  of  these  prob- 
lems is  at  present  further  advanced  than  the  second;  the  larger 
part  of  this  work  is,  therefore,  devoted  to  a  description  of  archi- 
tectural relations.  Without  a  knowledge  of  these  relations, 
moreover,  the  problems  of  metabohsm  are,  in  large  measure, 
meaningless. 

It  is  impossible  to  understand  clearly  the  form  of  the  brain, 
and  especially  the  relations  of  its  internal  structures,  from  verbal 
descriptions  merely.  Pictorial  illustrations  and  the  various  brain 
models  which  are  on  the  market  are  of  great  assistance;  but  ac- 
tual laboratory  experience  in  dissecting  the  brain  and,  if  possi- 
ble, the  study  of  microscopic  preparations  of  selected  parts  of 
it  are  indispensable  for  a  thorough  mastery  of  the  subject. 
The  brains  of  the  sheep,  dog,  and  cat  are  easily  obtained,  and 


PREFACE  13 

are  so  similar  to  the  human  brain  in  all  respects,  save  the 
smaller  relative  size  of  the  cerebral  cortex,  that  they  can  readily 
be  used  for  such  studies.  Before  dissection  the  brain  should  be 
carefully  removed  from  the  skull  and  hardened  by  immersion  for 
a  few  days  in  a  solution  of  formalin  (to  be  obtained  at  any  drug 
store  and  diluted  with  water  in  the  proportion  of  one  part 
formalin  to  nine  parts  water).  Several  neurological  laboratory 
guides  have  been  published,  and  one  of  these  should  be  followed 
in  the  dissection.^ 

This  work  is  designed  as  an  introduction  in  a  literal  sense. 
Several  very  excellent  manuals  and  atlases  of  neurology  are 
available,  and  to  these  the  reader  is  referred  for  the  illustrations 
and  more  detailed  descriptions  necessary  to  complete  the  rather 
schematic  outhne  here  presented.  The  larger  medical  text- 
books of  anatomy  and  physiology  are,  however,  often  very  diffi- 
cult for  the  beginner,  chiefly  on  account  of  the  lack  of  correlation 
of  the  structures  described  and  their  functions.  This  little 
book  has  been  prepared  in  the  hope  that  it  .will  help  the  student 
to  learn  to  organize  his  knowledge  in  definite  functional  pat- 
terns earlier  in  his  work  than  is  often  the  case,  and  to  appreciate 
the  significance  of  the  nervous  system  as  a  working  mechanism 
from  the  beginning  of  his  study. 

The  structure  and  functions  of  the  nervous  system  are  of 
interest  to  students  in  several  different  fields — medicine,  psy- 
chology, sociology,  education,  general  zoology,  comparative 
anatomy,  and  physiology,  among  others.  The  view-points  and 
special  requirements  of  these  various  groups  are,  of  course, 
different;  nevertheless  the  fundamental  principles  of  nervous 
structure  and  function  are  the  same,  no  matter  in  what 
field  the  principles  are  applied,  and  the  aim  here  has  been  to 

iBuRKHOLDER,  J.  F.  1912.  The  Anatomy  of  the  Brain,  Second  Edition, 
Chicago,  G.  P.  Engelhard  &  Co.      (Dissection  of  the  brain  of  the  sheep.) 

FisKE,  E.  W.  1913.  An  Elementary  Study  of  the  Brain  Based  on  the 
Dissection  of  the  Brain  of  the  Sheep,  New  York,  The  Macmillan  Company. 

Hardesty,  I.  1902.  Neurological  Teclmique,  The  University  of  Chicago 
Press.  (Dissection  of  the  human  brain  by  means  of  transverse  gross 
sections,  methods  of  microscopic  preparation,  and  lists  of  neurological 
terms.) 

Herrick,  C.  Judson,  and  Crosby,  Elizabeth.  191.5.  A  Laboratory 
Outline  in  Neurology,  privately  printed  by  the  authors  at  the  University  of 
Chicago.  (Dissection  of  the  dogfish,  sheep,  and  human  brains,  and  direc- 
tions for  study  of  prepared  microscopic  sections  of  the  human  brain.) 


14  PREFACE 

present  these  principles  rather  than  any  detailed  application 
of  them.  In  the  selection  of  subject  matter  and  mode  of 
treatment  the  author  has  been  fortunate  in  having  the  advice 
of  many  experienced  teachers  in  several  of  these  fields,  who 
have  read  the  manuscript  of  this  work  or  of  selected  chapters 
and  whose  suggestions  have  contributed  greatly  to  its  value. 
Especial  acknowlegement  of  generous  assistance  of  this  sort 
should  be  made  to  Doctors  G.  W.  Bartlemez,  R.  R.  Bensley, 
Harvey  A.  Carr,  C.  M.  Child,  G.  E.  Coghill,  Mabel  R.  Fernald, 
Joseph  W.  Hayes,  Mary  Stevens  Hayes,  F.  L.  Landacre,  John 
T.  McManis,  and  R.  E.  Sheldon. 

The  materials  presented  in  this  book  are  arranged  in  three 
groups:  (1)  Chapters  I  to  VII  discuss  the  more  general  neurologi- 
cal topics;  (2)  Chapters  VIII  to  XVIII  comprise  a  brief  account  of 
the  form  of  the  nervous  system  and  the  functional  significance  of 
its  chief  subdivisions  in  general,  followed  by  a  review  of  the  archi- 
tectural relations  of  the  more  important  functional  systems;  (3) 
Chapters  XIX  to  XXI  are  devoted  to  the  cerebral  cortex  and  its 
functions.  Readers  whose  chief  interest  lies  in  the  general  neu- 
rological questions  may  omit  much  of  the  detail  comprised 
within  the  second  group  of  chapters  or  use  these  for  reference 
only.  To  facilitate  ready  reference  the  general  index  has  been 
prepared  with  especial  care,  and  with  it  is  combined  a  brief 
glossary  of  some  more  commonly  used  technical  terms.  In  the 
text  some  of  the  more  special  topics,  which  may  be  omitted  if 
a  briefer  presentation  is  desired,  are  printed  in  smaller  type. 


C.   JuDSON   Herrick. 


Chicago,  III., 
October,  1915. 


CONTENTS 


CHAPTER   I  PAGE 

Biological  Introduction 17 

CHAPTER   n 

The  Nervous  Functions 24 

CHAPTER   HI 
The  Neuron 38 

CHAPTER   IV 
The  Reflex  Circuits 56 

CHAPTER  V 
The  Receptors  and  Effectors 69 

CHAPTER  VI 

The  General  Physiology  of  the  Nervous  System 96 

CHAPTER   VII 

The  General  Anatomy  and  Subdivision  of  the  Nervous  System  106 

CHAPTER  VIII 

The  Spinal  Cord  and  Its  Nerves 125 

CHAPTER   IX 
The  Medulla  Oblongata  and  Cerebellum 143 

CHAPTER   X 

The  Cerebrum 160 

15 


16  CONTENTS 

CHAPTER  XI 

PAGE 

The  General  Somatic  Systems  of  Conduction  Paths 172 

CHAPTER  XII 
The  Vestibular  Apparatus  and  Cerebellum 183 

CHAPTER  XIII 
The  Auditory  Apparatus 195 

CHAPTER  XIV 
The  Visual  Apparatus 204 

•     CHAPTER  XV 
The  Olfactory  Apparatus 215 

CHAPTER  XVI 

The  Sympathetic  Nervous  System 224 

CHAPTER  XVII 
The  Visceral  and  Gustatory  Apparatus 234 

CHAPTER  XVIII 
Pain  and  Pleasure 249 

CHAPTER  XIX 
The  Structure  of  the  Cerebral  Cortex 263 

CHAPTER  XX 
The  Functions  of  the  Cerebral  Cortex 279 

CHAPTER  XXI 

The  Evolution  and  Significance  of  the  Cerebral  Cortex 301 

Index  and  Glossary 317 


INTRODUCTION  TO   NEUROLOGY 


CHAPTER  I 

BIOLOGICAL   INTRODUCTION 

The  living  body  is  a  little  world  set  in  the  midst  of  a  larger 
world.  It  leads  in  no  sense  an  independent  life,  but  its  con- 
tinued welfare  is  conditioned  upon  a  nicely  balanced  adjust- 
ment between  its  own  inner  activities  and  those  of  surrounding 
nature,  some  of  which  are  beneficial  and  some  harmful.  The 
great  problem  of  neurology  is  the  determination  of  the  exact 
part  which  the  nervous  system  plays  in  this  adjustment. 

This  problem  is  by  no  means  simple.  The  search  for  its 
solution  will  lead  us,  in  the  first  place,  back  to  an  examination 
of  some  of  the  fundamental  properties  of  the  simplest  living 
substance,  of  protoplasm  itself;  and  in  the  last  analysis  it  will 
involve  a  consideration  of  the  highest  mental  capacities  of  the 
human  race  and  of  the  physiological  apparatus  through  which 
these  capacities  come  to  expression.  We  shall  first  take  up  the 
nature  of  this  adjustment  on  the  lower  biological  levels. 

All  of  the  infinitely  diverse  forms  of  li\'ing  things  have  cer- 
tain points  in  common,  so  that  one  rarely  has  any  doubt 
whether  a  given  object  is  alive  or  dead.  Nevertheless,  the 
precise  definition  of  life  itself  proves  very  difficult.  Herbert 
Spencer,  in  his  "Principles  of  Biology,"  after  many  pages 
of  close  argument  and  rather  formidable  verbal  gymnastics, 
arrived  at  this  formula:  Life  is  "the  definite  combination  of 
heterogeneous  changes,  both  simultaneous  and  successive,  in 
correspondence  with  external  coexistences  and  sequences"; 
or,  more  briefly,  "The  continuous  adjustment  of  internal  re- 
lations to  external  relations."     A  somewhat  similar  idea  was 

2  17 


18  INTRODUCTION  TO  NEUROLOGY 

subsequently  more  simply  expressed  by  the  late  C.  L.  Herrick 
in  the  proposition.  "Life  is  the  correlation  of  physical  forces 
for  the  conservation  of  the  individual";  and  this,  in  turn,  may 
be  cast  in  the  more  general  form,  Life  is  a  system  of  forces 
maintained  by  a  continuous  interchange  of  energy  between  the 
system  and  its  environment,  these  forces  being  so  correlated 
as  to  conserve  the  identity  of  the  system  as  an  individual  and 
to  propagate  it.  A  certain  measure  of  modifiability  in  the  char- 
acter of  the  system,  without  loss  of  its  individuality,  is  not  ex- 
cluded. 

No  one  of  these  definitions,  or  any  other  which  has  been  sug- 
gested, is  fully  satisfactory;  but  biologists  generally  agree  that 
the  common  characteristics  of  living  beings  can  best  be  ex- 
pressed in  the  present  state  of  our  knowledge  in  terms  of  their 
actions,  their  behavior.  The  properties  commonly  ascribed  to 
any  object  are  in  last  analysis  names  for  its  behavior,  and  the 
so-called  vital  properties  are  very  special  forms  of  energy  trans- 
formation. 

Now,  the  chief  difference  between  a  corpse  and  a  hving  body 
consists  in  the  fact  that  the  forces  of  surrounding  nature  tend 
to  the  disintegration  of  the  dead  body,  while  in  the  living  body 
these  forces  are  utilized  for  its  upbuilding.  If,  then,  the  vital 
process  is  essentially  a  special  type  of  mutual  interaction  be- 
tween the  bodily  mechanism  and  the  forces  of  the  surrounding 
world,  of  the  correspondence  between  the  organism  and  the 
environment,  to  use  the  Spencerian  phrase,  it  follows  that  the 
living  body  cannot  be  studied  by  itself  alone.  Quite  the  con- 
trary, the  analysis  of  the  environmental  forces  upon  which  the 
life  of  the  body  depends  and  of  the  parts  of  the  body  itself 
in  their  relations  to  these  external  forces  is  the  very  kernel  of 
the  problem  of  life. 

The  measure  of  the  fulness  of  life  in  any  organism  is  two- 
fold. In  the  first  place,  the  life  is  measured  by  the  amount  of 
energy  which  the  organism  can  assimilate  from  surrounding 
nature  and  incorporate  into  its  own  organization.  This  enters 
the  body  chiefly  in  the  form  of  chemical  potential  energy  in  food 
eaten,  air  breathed,  and  so  on,  and  can  be  quantitatively  de- 
termined and  stated  in  the  form  of  standard  units  of  energy, 
such  as  calories  or  foot-pounds  of  work.     This  measures  the 


BIOLOGICAL    INTRODUCTION  19 

working  capacity  of  the  machine,  but  gives  little  insight  into 
the  real  value  of  the  work  done.  In  the  second  place,  life  may 
be  measured  in  terms  of  the  extensity  or  number  and  diversity 
of  environmental  relations.  This  takes  account  of  the  range 
or  working  distance  of  the  organization  and,  in  general,  of  the 
efficiency  of  the  work  done.  For  evidently  the  organism  which 
has  few  and  simple  relations  with  the  environment,  so  that  it 
can  adjust  itself  to  only  a  small  range  of  external  conditions, 
is  less  efficient  than  one  which  has  many  diverse  relationships 
and  an  extensive  series  of  possible  adjustments,  even  though  the 
actual  amount  of  energy  expended  may  be  vastly  greater  in  the 
former  than  in  the  latter  case.  The  first  of  these  standards  is  a 
tolerably  satisfactory  measure  of  the  vegetative  functions  of 
the  body,  sometimes  less  happily  termed  the  "organic  functions." 
We  have  no  word  in  common  use  which  covers  precisely  the 
group  of  activities  embraced  by  our  second  standard  of  meas- 
urement, though  the  terms  "animal  functions,"  "somatic  or 
exteroceptive  activities"  are  sometimes  used  in  about  this 
sense. 

Let  us  now  endeavor  to  illustrate  the  last  topic  a  little  more 
concretely.  We  are  standing  on  a  hilltop  overlooking  a 
meadow,  through  which  runs  a  mountain  brook,  and  beyond 
the  valley  is  another  range  of  rugged  hills.  In  the  fence-corner 
near  us  is  a  patch  of  daisies  and  clover  with  a  honey-bee  buzzing 
from  flower  to  flower.  A  plowboy  is  crossing  the  field,  and  at 
our  elbow  an  artistic  friend  is  busy  with  sketching  pad  and 
brushes.  Here  are  four  things  which  have  this  at  least  in 
common,  that  they  are  alive — daisy,  bee,  plowboy,  artist. 
There  can  be  no  doubt  about  their  vitality,  but  how  differently 
they  respond  to  the  sunshine,  the  rain,  and  the  other  forces  of 
nature. 

The  daisy  expands  in  the  vivifying  light  of  the  summer  sun, 
the  energy  of  whose  actinic  rays  is  used  to  build  up  living  proto- 
plasm and  vegetable  fiber  from  the  inert  substances  of  air  and 
soil.  Its  vitality,  measured  in  terms  of  energy  transforma- 
tion, is  great;  yet  how  limited  its  range  of  life,  how  helpless  in 
the  face  of  the  storms  of  adversity  which  are  sure  to  bufi'et  it. 
Rooted  to  its  station,  it  can  only  assimilate  what  food  is  brought 
to  it  and  it  cannot  flee  from  scorching  wind  or  bfighting  frost. 


20  INTRODUCTION  TO  NEUROLOGY 

The  honey-bee  leads  a  more  free  and  varied  hfe.  Instead  of 
passively  and  blindly  waiting  for  such  bane  or  blessing  as  fate 
may  bring,  she  hurries  forth,  strong  of  wing  and  with  senses 
alert,  to  gather  the  daily  measure  of  honey  and  pollen.  The 
senses  of  touch,  sight,  and  smell  open  realms  of  nature  forever 
closed  to  the  plant,  and  enable  her  to  seek  food  in  new  fields 
when  the  local  supply  is  exhausted,  as  well  as  to  avoid  enemies 
and  misfortunes.  With  the  approach  of  the  storm,  she  flies  to 
shelter  in  a  home  which  she  and  her  sisters  have  prepared  with 
consummate  skill.  Yet  in  this  provision  for  the  future  in  hive 
and  well-stocked  honeycomb  there  is  little  evidence  of  intelli- 
gent foresight  or  rational  understanding  of  the  purposes  for 
which  they  work.  Though  so  much  more  highly  organized  than 
the  plant,  the  honey-bee  is  to  a  very  large  extent  blindly  follow- 
ing out  the  inborn  impulses  of  her  hereditary  organization  and 
she  has  no  clear  understanding  of  what  she  does,  much  less  why 
she  does  it.  There  is  some  evidence  of  intelligent  adaptation  in 
her  behavior,  but  the  part  played  by  this  factor  in  her  life  as  a 
whole  is  probably  very  small  compared  with  the  blind  inborn 
impulses  which  dominate  most  of  her  activities.  Like  the  plant, 
the  bee's  reactions  are  determined  chiefly  by  the  past  evo- 
lutionary history  of  the  species,  which  has  shaped  the  innate 
organization  of  the  body  and  flxed  its  typical  modes  of  re- 
sponse to  stimulation.  But  the  bee  lives  much  more  in  the 
present  than  does  the  plant;  that  is,  she  can  vary  her  behavior 
much  more  widely  in  response  to  the  needs  of  the  moment.  As 
for  the  future,  she  knows  naught  of  it. 

The  farmer's  boy  whistles  as  he  goes  about  his  work.  He, 
too,  has  a  certain  innate  endowment,  including  the  whole 
range  of  his  vegetative  functions,  together  with  an  instinctive 
love  of  sport  and  many  other  inborn  aptitudes.  This  is  his 
inheritance  from  the  past.  By  these  instincts  and  appetites  he 
is,  as  Dewey  says,  "pushed  from  behind"  through  the  per- 
formance of  many  blindly  impulsive  acts.  He  is  a  creature  of 
the  present,  too,  his  whole  nature  overflowing  with  the  joy  of 
living.  But  he  also  looks  into  the  future  and  hastens  through 
the  daily  tasks  that  he  may  obtain  the  coveted  hour  of  sunset 
to  fish  in  the  brook.  He  flicks  off  the  heads  of  the  daisies  with 
his  whip-stock   and   remarks  in   passing,     "This  meadow  is 


BIOLOGICAL    INTRODUCTION  21 

choking  up  with  white-weed.  The  boss  will  have  to  plow  it  up 
next  year  and  replant  it."  The  extraordinary  natural  beauty 
of  the  place  is,  however,  unnoticed  amid  the  round  of  daily 
work  and  simple  pleasure. 

The  artist  looks  out  upon  the  same  scene,  but  through  what 
different  eyes!  The  mass  of  white  daisies  and  the  rocky  knoll 
beyond  ruddy  with  sheep  sorrel  suggest  to  him  no  waste  of 
valuable  pasture  land,  but  a  harmony  of  color  and  grace  of  form 
upon  which  he  feasts  his  soul.  The  esthetic  dehghts  of  the 
forest,  the  sky,  the  brook,  and  the  overhanging  crag  beyond  are 
for  him  unmixed  with  any  utilitarian  motive. 

Each  of  these  four  organisms  occupies,  in  one  sense,  the 
same  environment;  but  it  is  evident  that  the  factors  of  this 
environment  with  which  each  comes  into  active  vital  relations 
are  immeasurably  different.  They  correspond  with  or  are  at- 
tuned to  quite  different  energy  complexes,  though  the  cor- 
respondence or  interaction  is  very  real  in  each  case.  This  has 
been  stated  very  simply  by  Dr.  Jennings  when  he  says  that 
every  species  of  organism  has  its  characteristic  ''action  system," 
i.  e.,  a  habitual  mode  of  reaction  to  its  environment  which  is 
determined  wholly  or  in  part  by  its  inherited  organization. 

Every  animal  and  every  plant  has,  accordingly,  a  definite 
series  of  characteristic  movements  which  it  can  make  in  re- 
sponse to  external  stimulation.  This  is  all  that  Jennings  means 
by  the  "action  system."  We  humans  are  no  exception  to  this 
rule  of  life.  We  move  along  in  a  more  or  less  stereotyped  way, 
through  more  or  less  familiar  grooves,  in  our  daily  work. 
Much  of  this  work  is  routine,  done  about  as  mechanically  as 
the  flower  unfolds  its  petals  to  the  morning  sun  or  the  honey- 
bee gathers  in  her  store  of  honey.  This  is  our  action  system. 
Of  course,  we  have  much  else  to  do  besides  this  routine,  and  our 
actual  value  to  the  community  is  in  large  measure  determined  by 
our  ability  to  vary  this  routine  in  adaptation  to  new  situations 
as  they  arise.  Even  the  daisy  has  a  little  of  this  capacity  for 
independently  variable  action;  the  insect  has  more;  and  man's 
preeminence  in  the  world  is  due  primarily  to  his  larger  powers 
of  adapting  his  reactions  not  only  to  the  needs  of  the  moment, 
but  to  probable  future  contingencies,  i.  e.,  of  varying  his 
inborn  action  system  by  intelligently  directed  choices. 


22  INTRODUCTION  TO  NEUROLOGY 

This  distinction  between  the  bUnd  working  of  a  stereotyped 
action  system  whose  character  is  determined  by  the  inherited 
bodily  structure,  on  the  one  hand,  and  individually  acquired 
variable  adaptive  actions  (which  may  or  may  not  be  intelli- 
gently performed),  on  the  other  hand,  is  very  fundamental,  and 
we  shall  have  occasion  to  return  to  it.  Most  animal  activities 
contain  both  of  these  factors,  and  it  is  often  very  difficult 
to  analyze  a  given  example  of  behavior  into  its  elements, 
but  the  distinction  is  nevertheless  important.  Plant  life  is 
characterized  by  the  dominance  of  invariable  types  of  reaction 
which  are  determined  by  innate  structure;  these  in  their  most 
elementary  forms  give  us,  in  fact,  the  so-called  vegetative  func- 
tions. These  same  functions  predominate  in  the  lowest  animals 
also;  but  in  the  higher  animals,  as  we  shall  see,  there  are  two 
rather  distinct  lines  of  evolutionary  advance.  In  one  line  the 
innate  stereotyped  functions  are  very  highly  specialized,  leading 
up  to  a  complex  instinctive  mode  of  life;  in  the  other  line  these 
functions  are  subordinated  to  a  higher  development  of  the  indi- 
vidually acquired  variable  functions,  leading  up  to  the  intelli- 
gence and  docility  of  the  higher  mammals,  including  the  human 
race. 

The  distinction  between  plants  and  animals  is  very  difficult 
to  draw  and,  in  fact,  there  are  numerous  groups  of  organisms 
which  at  the  present  time  occupy  an  ambiguous  position,  such 
as  the  slime  molds.  The  botanists  claim  them  and  call  them 
Myxomycetes;  the  zoologists  also  describe  them  under  the  name 
Mycetozoa;  still  other  naturalists  frankly  give  up  the  problem 
and  assign  them  to  an  intermediate  kingdom,  neither  vegetable 
nor  animal,  which  they  call  the  Protista.  As  children  we  prob- 
ably considered  the  chief  distinction  between  plants  and  ani- 
mals to  be  the  ability  of  the  latter  to  move  freely  about;  but  one 
of  the  first  lessons  in  our  elementary  biology  was  the  correction 
of  this  notion  by  the  study  of  sedentary  animals  and  motile 
plants.  Nevertheless,  I  fancy  that  in  the  broad  view  the  child- 
ish idea  has  the  root  of  the  matter  in  it.  The  plants  and  seden- 
tary animals  may  have  their  vegetative  functions  of  internal 
adjustment  never  so  highly  specialized  and  yet  remain  rela- 
tively low  in  the  biological  scale  because  their  relations  with 
the  environment  are  necessarily  limited  to  the  small  circle  within 


BIOLOGICAL    INTRODUCTION  23 

which  tliey  first  take  root,  whereas  the  power  of  locomotion 
carries  with  it,  at  least  potentially,  the  ability  to  choose  between 
many  more  environmental  factors.  It  is  only  the  free-moving 
animals  that  have  anything  to  gain  by  looking  ahead  in  the 
world,  and  here  only  do  we  find  well-developed  distance  recep- 
tors, i.  e.,  sense  organs  adapted  to  respond  to  impressions  from 
objects  remote  from  the  body.  And  the  distance  receptors,  as 
we  shall  see,  have  dominated  the  evolution  of  the  nervous  sys- 
tem in  vertebrates  and  determined  the  lines  it  should  follow. 

The  net  result  of  this  discussion  can  be  briefly  stated.  The 
differences  between  various  kinds  of  organisms  are,  in  the  main, 
incidental  to  the  extent  and  character  of  their  relations  with  the 
forces  of  surrounding  nature.  A  species  which  can  adjust  itself 
to  few  elements  of  its  environment  we  call  low;  one  that  can 
adapt  itself  to  a  wide  range  of  environmental  conditions  in  a 
great  variety  of  ways  we  call  higher.  The  supremacy  of  the 
human  race  is  directly  due  to  our  capacity  for  diversified  living. 
If  man  finds  himself  in  an  unfavorable  climate,  he  may  either 
move  to  a  more  congenial  locality  or  adapt  his  mode  of  life  by 
artificial  aids,  such  as  clothing,  houses,  and  fire.  And  in  these 
adaptations  he  is  not  limited  to  a  narrow  range  of  inherited 
instincts,  like  the  hive  of  bees,  but  his  greater  powers  of  obser- 
vation and  reflection  enable  him  to  discover  the  general  uni- 
formities of  natural  process  (he  calls  these  laws  of  nature)  and 
thus  to  forecast  future  events  and  prepare  himself  for  them  in- 
telligently. In  other  words,  to  return  to  our  original  point  of 
view,  our  advantage  in  the  struggle  for  existence  lies  in  our 
ability  to  correlate  our  bodily  activities  with  a  wide  range  of 
natural  forces  so  as  to  make  use  of  these  forces  for  our  good  rather 
than  our  hurt.  (Of  course,  it  should  be  borne  in  mind  that  this 
formula  makes  no  pretense  of  being  an  exhaustive  account  of 
human  faculty;  but  only  that,  in  so  far  as  biological  evolutionary 
factors  have  operated  in  the  human  realm,  they  act  in  accord- 
ance with  this  principle.)  The  apparatus  by  which  these  exter- 
nal adjustments  are  effected  and  by  which  the  inner  parts  of  the 
body  are  kept  in  working  order  is  the  nervous  system. 


CHAPTER  II 

THE  NERVOUS  FUNCTIONS 

The  body  is  composed  of  organs  and  tissues,  the  organs  being 
parts  with  particular  functions  to  perform  and  the  tissues  being 
tlie  cellular  fabric  of  which  the  organs  are  composed.  The 
tissues  (which  must  be  studied  microscopically)  are  classified, 
sometimes  in  accordance  with  the  general  functions  which  they 
serve,  such  as  the  nervous  and  muscular  tissues,  and  sometimes 
with  reference  to  the  forms  and  arrangements  of  their  compo- 
nent cells.  An  illustration  of  the  latter  method  of  treatment  is 
furnished  by  the  epithelial  tissues,  which  are  thin  sheets  of 
cells,  sometimes  arranged  in  one  layer  (simple  epithelia),  some- 
times in  several  layers  (stratified  epithelia).  Epithelial  tissues 
may  perform  the  most  diverse  functions. 

All  living  substance  (protoplasm)  possesses  in  some  measure 
the  distinctive  nervous  functions  of  sensitivity  and  conductivity, 
that  is,  it  responds  in  a  characteristic  fashion  to  certain  exter- 
nal forces  (stimuli),  and  when  thus  stimulated  at  one  point  the 
movement  or  other  response  may  be  effected  by  some  remote 
part.  This  last  feature  implies  that  some  form  of  energy  is 
conducted  from  the  site  of  the  stimulus  to  the  part  moved. 
Ordinary  protoplasm  also  possesses  the  power  of  correlation, 
that  is,  of  combining  a  number  of  individual  reactions  to  stimu- 
lation in  diverse  special  adjustments. 

The  one-celled  animals  and  all  plants  lack  the  nervous  sys- 
tem entirely;  nevertheless  they  are  able  to  make  highly  complex 
adjustments.  The  leaves,  roots,  and  stems  of  the  higher  plants 
have  individual  functions  which  are,  however,  bound  together 
or  integrated  into  a  very  perfect  unity.  In  animals,  as  con- 
trasted with  plants,  we  see  a  further  differentiation  of  parts  of 
the  body  for  special  functions,  and  at  the  same  time  a  more  per- 
fect correlation  of  part  with  part  and  integration  of  the  whole 
for  rapid  and  diversified  reactions  of  the  entire  body.     The 

24 


THE    NERVOUS    FUNCTIONS  25 

nervous  system  is  the  apparatus  of  these  more  perfect  adjust- 
ments and  its  protoplasm  is  highly  modified  in  different  direc- 
tions. Some  parts  may  be  especially  sensitive  to  particular 
forms  of  energy  (such  as  light  waves,  sound  waves,  etc.,  this 
being  termed  the  adequate  stimulus  in  each  case) ;  other  parts, 
the  nerves,  are  highly  modified  so  as  to  conduct  nervous  impulses 
from  part  to  part  with  a  minimum  expenditure  of  energy  and  loss 
of  efficiency;  still  other  parts  of  the  nervous  system  serve  as 
centers  for  receiving  and  redistributing  nervous  impulses  some- 
what after  the  fashion  of  the  central  exchange  of  an  automatic 


Fig.  1. — Diagram  illustrating  the  simplest  spinal  reflex  arc  consisting 
of  two  nervous  elements  or  neurons  (see  Chapter  III),  a  sensory  neuron 
connected  with  the  skin  and  a  motor  neuron  connected  with  a  muscle. 
Physiological  connection  between  the  two  neurons  is  effected  within  the 
spinal  cord.     (Modified  from  Van  Gehuchten.) 

telephone  system.  These  are  the  correlation  centers,  and  they 
are  larger  and  more  complex  in  proportion  to  the  range  of  diver- 
sity in  the  possible  reactions  of  the  animal. 

The  simpler  reactions  to  stimulation  of  the  sort  here  under  con- 
sideration are  called  reflexes  (Fig.  1 ;  see  also  p.  56),  and  the  essen- 
tial mechanism  is  a  reflex  arc  consisting  of  (1)  a  sensitive  receiv- 
ing organ  (receptor  or  sense  organ);  (2)  a  conductor  (aff"erent 
or  sensory  nerve)  transmitting  the  nervous  impulse  inward  from 
the  receptor;  (3)  a  correlation  center  or  adjuster,  generally 
located  within  the  central  nervous  system;  (4)  a  second  con- 
ductor (efferent  or  motor  nerve)  transmitting  the  nervous  im- 


26  INTRODUCTION   TO    NEUROLOGY 

pulse  outward  from  the  center  to  (5)  the  effector  apparatus, 
consisting  of  the  organs  of  response  (muscles,  glands)  and  the 
terminals  of  the  efferent  nerves  upon  them. 

No  part  of  the  nervous  system  has  any  significance  apart  ft'om 
the  peripheral  receptor  and  effector  apparatus  with  which  it  is 
functionally  related.  This  is  true  not  only  of  the  nervous  mech- 
anism of  all  physiological  functions,  but  even  of  the  centers  con- 
cerned with  the  highest  manifestations  of  thought  and  feeling  of 
which  we  are  capable,  for  the  most  abstract  mental  processes 
use  as  their  necessary  instruments  the  data  of  sensory  experience 
directly  or  indirectly,  and  in  many,  if  not  all,  cases  are  inti- 
mately bound  up  with  some  form  of  peripheral  expression. 

The  neurologist's  problem  is  to  disentangle  the  inconceivably 
complex  interrelations  of  the  nerve-fibers  which  serve  all  the 
manifold  functions  of  adjustment  of  internal  and  external  rela- 
tions; to  trace  each  functional  system  of  fibers  from  its  appro- 
priate receptive  apparatus  (sense  organ)  to  the  centers  of  corre- 
lation; to  analyze  the  innumerable  nervous  pathways  by  which 
these  centers  are  connected  with  each  other  (correlation  tracts) ; 
and,  finally,  to  trace  the  courses  taken  by  all  outgoing  impulses 
from  these  correlation  centers  to  the  peripheral  organs  of  re- 
sponse (muscles,  glands,  etc.,  or,  collectively,  the  effectors). 

This  is  no  simple  task.  If  it  were  possible  to  find  an  educated 
man  who  knew  nothing  of  electricity  and  had  never  heard  of  a 
telegraph  or  telephone,  and  if  this  man  were  assigned  the  duty 
of  making  an  investigation  of  the  telegraph  and  telephone  sys- 
tems of  a  great  city  without  any  outside  assistance  whatever, 
and  of  preparing  a  report  upon  all  the  physical  equipment  with 
detailed  maps  of  all  stations  and  circuits  and  with  an  explana- 
tion of  the  method  of  operation  of  every  part,  his  task  would  be 
simple  compared  with  the  problem  of  the  neurologists.  The 
human  cerebral  cortex  alone  contains  some  9280  million  nerve- 
cells,  most  of  which  are  provided  with  long  nerve-fibers  which 
stretch  away  for  great  distances  and  branch  in  different  direc- 
tions, thus  connecting  each  cell  with  many  different  nerve- 
centers.  The  total  number  of  possible  nervous  pathways  is, 
therefore,  inconceivably  great. 

Fortunately  for  the  neurologists,  these  interconnecting  ner- 
vous pathways  do  not  run  at  random;  but,  just  as  the  wires 


THE    NERVOUS    FUNCTIONS  27 

entering  a  telephone  exchange  are  gathered  together  in  great 
cables  and  distributed  to  the  switchboards  in  accordance  with  a 
carefully  elaborated  system,  so  in  the  body  nerve-fibers  of  like 
function  tend  to  run  together  in  separate  nerves  or  within  the 
brain  in  separate  bundles  called  tracts.  Notwithstanding  the 
complexity  of  organization  of  the  nervous  organs,  the  larger  and 
more  important  functional  systems  of  nervous  pathways  have 
been  successfully  analyzed,  and  the  courses  of  nervous  discharge 
from  the  various  receptors  to  the  appropriate  centers  of  adjust- 
ment, and  from  these  (after  manifold  correlations  with  other  sys- 
tems) to  the  organs  of  response,  are  fairly  well  known.  The 
acquisition  of  this  knowledge  has  required  several  centuries  of 
painstaking  anatomical  and  physiological  study,  and  much 
remains  yet  to  be  done. 

The  external  forms  of  the  brain  and  other  parts  of  the  nervous 
system  are  dependent  mainly  upon  the  arrangements  of  the 
nerve-cells  of  which  they  are  composed  (for  the  characteristics  of 
these  cells  see  Chapter  III),  and  these  arrangements,  in  turn, 
are  correlated  with  the  functions  to  be  performed.  The  func- 
tional connections  of  the  nerve-cells  can  be  investigated  best  by 
the  microscopical  studj^  of  the  tissues  combined  with  physiolog- 
ical experimentation.  From  this  it  follows  that  the  study  of  the 
gross  anatomy,  the  microscopical  anatomy  (histology),  and  the 
physiology  of  the  nervous  sj^stem  should  go  hand  in  hand  so  far 
as  this  is  practicable. 

A  study  of  the  comparative  anatomy  of  the  nervous  system 
shows  that  its  form  is  always  correlated  with  the  behavior  of  the 
animal  possessing  it.  The  simplest  form  of  nervous  system  con- 
sists of  a  diffuse  network  of  nerve-cells  and  connecting  fibers 
distributed  among  the  other  tissues  of  the  body.  Such  a  ner- 
vous system  is  found  in  some  jelly-fishes  and  in  parts  of  the 
sympathetic  nervous  system  of  higher  animals.  Animals  which 
possess  this  diffuse  type  of  nervous  system  can  perform  only 
very  simple  acts,  chiefly  total  movements  of  the  whole  body 
or  general  movements  of  large  parts  of  it,  with  relatively  small 
capacity  for  refined  activities  requiring  the  cooperation  of 
many  different  organs.  But  even  the  lowest  animals  which 
possess  nerves  show  a  tendency  for  the  nervous  net  to  be  con- 
densed in  some  regions  for  the  general  control  of  the  activities 


28 


INTRODUCTION   TO   NEUROLOGY 


of  the  different  parts  of  the  body.  Thus  arose  the  central  ner- 
vous system.  (Some  works  dealing  with  the  evolution  of  the 
nervous  system  are  cited  at  the  end  of  this  chapter.) 

The  aggregations  of  nervous  tissue  to  which  reference  has  just 
been  made,  containing  the  bodies  of  the  nerve-cells,  are  called 
ganglia,^  and  in  all  invertebrate  animals  the  central  nervous 
system  is  a  series  of  such  ganglia,  variously  arranged  in  the  body 
and  connected  by  strands  containing  nerve-fibers  only,  that  is, 
by  nerves. 


Superior  ganglia 
Pharynx 
Inferior  ganglia 


Ventral  ganglia 


Fig.  2. — The  anterior  end  of  an  earthworm  (Lumbricus)  laid  open  from 
above  with  all  of  the  organs  dissected  away  except  the  ventral  body  wall 
and  ventral  ganglionic  chain. 


The  central  nervous  systems  of  all  but  the  lowest  forms  of 
animals  are  developed  in  accordance  with  two  chief  structural 
patterns,  represented  in  typical  form  by  the  worms  and  insects 
on  the  one  hand,  and  by  the  back-boned  animals  or  vertebrates 
on  the  other  hand. 

In  the  segmented  worms  (such  as  the  common  earthworm, 
Fig.  2)  the  central  nervous  system  consists  of  a  chain  of  ganglia 
connected  by  a  longitudinal  cord  along  the  lower  or  ventral  wall 

^  On  the  ganglia  of  the  vertebrate  nervous  system,  see  page  108. 


THE    NERVOUS    FUNCTIONS  29 

of  the  body.  Each  of  these  gangUa  is  connected  by  means  of 
peripheral  nerves  with  the  skin  and  muscles  of  its  own  segment, 
and  each  joint  of  the  body  with  its  contained  ganglion  (ventral 
ganglion)  has  a  certain  measure  of  physiological  independence  so 
that  it  can  act  as  a  unit.  This  is  a  typical  segmented  nervous 
system.  At  the  head  end  of  the  body  the  ventral  ganglionic 
chain  divides  around  the  pharynx  and  mouth,  and  there  are 
enlarged  ganglia  above  and  below  the  pharynx.  The  superior 
ganglia  (supra-esophageal  ganglia)  are  sometimes  called  the 
brain,  and  this  organ  dominates  the  local  activities  of  the  several 
segments,  enabling  the  animal  to  react  as  a  whole  to  external 
influences. 

The  nervous  systems  of  crustaceans  (crabs  and  their  allies), 
spiders,  and  insects  have  been  derived  from  the  type  just 
described.  In  these  animals  the  segments  of  the  body  are  more 
or  less  united  in  three  groups,  constituting  respectively  the  head, 
thorax,  and  abdomen,  and  the  ganglia  of  the  central  nervous 
system  are  modified  in  a  characteristic  way  in  each  of  these 
regions.  Figure  3  illustrates  the  nervous  systems  of  four  species 
of  flies,  showing  different  degrees  of  concentration  of  the  ganglia. 
In  all  cases  the  head  part  (brain)  is  greatly  enlarged,  and  is 
arranged,  as  in  worms,  in  ganglia  above  and  below  the  mouth 
and  esophagus.  The  other  gangha  are  diversely  arranged,  from 
the  simple  condition  (A)  where  there  are  three  thoracic  ganglia, 
one  for  each  pair  of  legs,  and  six  abdominal  ganglia,  through  in- 
termediate stages  (B  and  C),  to  the  highest  form  (D),  where  all 
of  the  ganglia  of  both  thorax  and  abdomen  are  united  in  a  single 
thoracic  mass. 

The  type  of  nervous  system  just  described  is  found  throughout 
the  highest  groups  of  invertebrate  animals,  as  in  insects  and 
spiders,  and  is  constructed  on  a  totally  different  plan  from  that 
of  all  of  the  vertebrate  or  back-boned  animals.  In  this  latter 
group  we  have,  instead  of  a  segmented  chain  of  ventrally  placed 
solid  ganglia,  a  hollow  tube  of  nervous  tissue  which  extends 
along  the  back  or  dorsal  wall  of  the  body  and  constitutes  the 
spinal  cord  and  brain.  The  cavity  or  lumen  of  this  tube  extends 
throughout  the  entire  length  of  the  central  nervous  system, 
forming  the  ventricles  of  the  brain  and  the  central  canal  of  the 
spinal  cord.     The  details  of  the  invertebrate  nervous  systems 


30 


INTRODUCTION   TO    NEUROLOGY 


(whose  structures  are  very  diverse)  will  not  be  further  consid- 
ered in  this  work;  the  nervous  systems  of  all  vertebrates,  how- 
ever, are  constructed  on  a  common  plan,  and,  though  our  prime 
interest  is  the  analysis  of  the  human  nervous  system,  we  shall 
find  that  many  of  the  details  sought  can  be  seen  much  more 
clearly  in  the  lower  vertebrates  than  in  man. 


Fig.  3. — The  nervous  systems  of  four  species  of  flies,  to  illustrate  the 
various  degrees  of  concentration  of  the  ganglia:  A,  Chrionomus  plumosus, 
with  three  thoracic  and  six  abdominal  ganglia;  B,  Empis  stercorea,  with 
two  thoracic  and  five  abdominal  ganglia;  C,  Tabanus  bovinus,  with  one 
thoracic  ganglion  and  the  abdominal  ganglia  moved  toward  each  other;  D, 
Sarcophaga  carnaria,  with  all  thoracic  and  abdominal  ganglia  united  into 
a  single  mass.  (After  Brand,  from  Lang's  Text-book  of  Comparative 
Anatomy.) 


Correlated  with  these  differences  between  the  structure  of 
invertebrate  and  vertebrate  nervous  systems  there  are  equally 
fundamental  differences  in  the  behavior  of  these  animals  which 
require  a  few  words  of  further  explanation.  Living  substance 
exhibits  as  its  most  fundamental  characteristic,  as  we  saw  at  the 
beginning,  the  capacity  of  adjusting  its  own  activities  to  con- 
stantly changing  environmental  conditions  in  such  a  way  as  to 
promote  its  own  welfare.     This  adjustment  may  be  effected 


THE    NERVOUS    FUNCTIONS  31 

in  two  waA's,  l^oth  of  which  arc  universally  present  and  which 
throuo'hout  the  remainder  of  this  work  we  shall  call  the  inmriahle 
or  innate  behavior  and  the  variable  or  individually  modifiable 
behavior. 

Every  animal  reaction,  then,  contains  .these  two  factors,  the 
invariable  and  the  variable  or  individually  modifiable.  The 
first  factor  is  a  function  of  the  relatively  stable  organization  of 
the  particular  living  substance  involved.  The  pattern  of  this 
organization  is  inherited,  and  these  characteristics  of  the  be- 
havior are,  therefore,  common,  except  for  relatively  slight  devia- 
tions, to  all  members  of  the  race  or  species;  they  are  rigidly 
determined  by  innate  bodily  organization  so  arranged  as  to 
facilitate  the  appropriate  reactions,  in  an  invariable  mechanical 
fashion,  to  every  kind  of  stimulation  to  which  the  organism 
is  capal^le  of  responding  at  all.  In  the  strictly  vegetative  func- 
tions, in  all  true  reflexes  (as  these  are  defined  on  page  56),  and  in 
purely  instinctive  activities  in  general  this  factor  of  behavior  is 
dominant. 

But  in  addition  to  this  invariable  innate  behavior,  all  organ- 
isms have  some  power  to  modify  their  characteristic  action  sys- 
tems in  adaptation  to  changed  environmental  relations.  This 
individual  modifiability  is  known  as  biological  regulation,  a  proc- 
ess which  has  of  late  been  very  carefully  studied.  We  cannot 
here  enter  into  the  problems  connected  with  form  regulation, 
that  is,  the  power  of  an  organism  to  restore  its  normal  form  after 
mutilation  or  other  injury.  On  regulation  in  behavior  reference 
should  be  made  to  the  works  of  Jennings  and  Child.  In  lower 
organisms  Jennings  recognizes  three  factors  in  the  regulation  of 
behavior:  First,  the  occurrence  of  definite  internal  processes; 
these  form  part  of  the  invariable  hereditary  action  system  re- 
ferred to  above.  Second,  interference  with  these  processes 
causes  a  change  of  behavior  and  varied  movements,  subjecting 
the  organism  to  many  different  conditions.  Third,  one  of  these 
conditions  may  relieve  the  interference  with  the  internal  proc- 
esses, so  that  the  changes  in  behavior  cease  and  the  relieving 
condition  is  thus  retained.  Lack  of  oxygen,  for  instance,  would 
interfere  with  an  animal's  internal  processes;  this  leads  it  to  move 
about;  if  finallv  it  enters  a  region  plentifully  supplied  with  oxy- 
gen, the  internal  processes  return  to  normal,  the  movement 


32  INTRODUCTION  TO   NEUROLOGY 

ceases,  and  the  animal  again  settles  down  to  rest.  If  this  regu- 
latory process  is  oft  repeated  another  factor  enters,  viz.,  the 
facilitation  of  a  given  adjustment  by  repetition.  Thus  arise 
physiological  habits  or  acquired  automatisms. 

The  more  highly  complex  forms  of  individual  modifiability 
are  termed  associative  memory  and  intelligence,  and  the  latter 
of  these  is  by  definition  consciously  performed.  Whether  con- 
sciousness is  present  in  the  simpler  forms  of  "associative  memory" 
as  these  are  demonstrated  by  students  of  animal  behavior  in 
lower  animals  cannot  be  positively  determined.  In  the  behavior 
of  lower  animals  there  are  no  criteria  which  enable  us  to  tell 
whether  a  given  act  is  consciously  performed  or  not,  and,  there- 
fore, the  lower  limits  of  intelhgence  in  the  animal  kingdom  are 
problematical.  In  other  words,  the  manifestations  of  variable 
behavior  form  a  graded  series  from  the  simple  regulatory  phe- 
nomena of  unicellular  organisms,  as  illustrated  above,  to  the 
highest  human  intelligence,  so  far  as  these  express  themselves 
objectively. 

In  mankind,  where  intelligent  behavior  is  dominant,  the 
stereotyping  of  the  adjustments  by  repetition  (true  habit  forma- 
tion) may  also  take  place,  and  in  this  case  the  acquired  au- 
tomatisms are  sometimes  said  to  arise  by  "lapsed  intelligence," 
that  is,  an  act  which  has  been  consciously  learned  may  ulti- 
mately come  to  be  performed  mechanically  and  nearly  or  quite 
unconsciously.  Much  of  the  process  of  elementary  education 
is  concerned  with  the  establishment  of  such  habitual  reactions  to 
frequently  recurring  situations.  How  far  "lapsed  intelligence" 
is  represented  in  the  so-called  instincts  of  other  animals  is  still 
a  debated  question  (see  p.  301). 

Among  the  invertebrate  animals,  the  insects  and  their  allies 
possess  a  bodily  organization  which  favors  the  performance  of 
relatively  few  movements  in  a  very  perfect  fashion,  that  is,  the 
action  system  is  simple  but  highly  perfected  within  its  own  range. 
Their  reflexes  and  instincts  are  very  perfectly  performed,  but 
the  number  of  such  reactions  which  the  animal  can  make  is  rather 
sharply  limited  and  fixed  by  the  inherited  bodily  structure. 
Their  behavior  is  dominated  by  the  invariable  and  innate  fac- 
tors and  they  cannot  readily  adapt  themselves  to  unusual  condi- 
tions.    The  vertebrates  likewise  have  many  elements  of  their 


THE    NERVOUS    FUNCTIONS  33 

behavior  which  are  similarly  fixed  or  stereotyped  in  their  innate 
organization;  but,  in  addition  to  these  stable  reflexes  and  in- 
stincts, the  higher  members  of  this  group  have  also  a  consider- 
able capacity  for  individual  modifiabilit}-  in  behavior,  and  they 
are  characterized  by  greater  individual  plasticity  and  docility 
(Yerkes).  It  appears  that  the  tubular  type  of  nervous  system 
found  in  vertebrates  permits  of  the  development  of  certain 
kinds  of  correlation  mechanisms  which  are  impossible  in  the  more 
compact  form  of  ganglia  of  the  insects.  These  two  branches  of 
the  animal  kingdom  have,  therefore,  during  all  of  the  more 
recent  evolutionary  epochs  diverged  farther  from  each  other, 
and  now,  in  their  highly  differentiated  conditions,  neither  type 
could  be  derived  from  the  other.  The  jointed  animals  (articu- 
lates) developed  from  the  lower  worms,  and  this  branch  of  the 
animal  kingdom,  which  may  be  called  the  articulate  phylum, 
culminates  in  the  insects.  The  vertebrates  were  probably 
developed  from  similar  lowly  worm-like  forms  along  an  inde- 
pendent line  of  evolution,  and  this  branch  of  the  animal  king- 
dom, the  vertebrate  phylum,  culminates  in  the  human  race. 
Figure  4  illustrates  in  a  rough  diagrammatic  way  the  relative  de- 
velopment of  the  variable  and  invariable  factors  of  behavior  in 
the  articulate  and  vertebrate  phjda. 

In  unicellular  organisms  without  nervous  systems  the  general 
protoplasm,  of  course,  is  the  apparatus  of  both  the  invariable 
and  the  variable  factors  of  behavior,  and  the  simpler  forms  of 
nervous  sj^stem  likewise  possess  both  of  these  capacities.  But 
in  the  more  complex  forms  of  nervous  system  among  vertebrates 
special  correlation  centers  are  set  apart  for  the  variable  activi- 
ties, particularly  those  which  are  intelhgently  performed,  and 
the  most  important  of  these  centers  are  found  in  the  cerebral 
cortex.  This  is  the  part  of  the  brain  which  is  greatly  enlarged  in 
mankind,  as  contrasted  with  all  other  animals,  and  the  last  three 
chapters  of  this  work  are  devoted  to  the  structure  and  functions 
of  these  cortical  mechanisms  with  whose  activity  the  progress  of 
human  culture  is  so-  intimately  related. 

It  should  be  borne  in  mind  that  the  higher  correlation  centers 

which  serve  the  individually  variable  or  labile  behavior  in  higher 

vertebrates  can  act  only  through  the  agency  of  the  lower  reflex 

centers.     The  point  is,  that  all  of  the  elements  of  behavior  are 

3 


34 


INTRODUCTION   TO    NEUROLOGY 


represented  in  the  innate  neuro-muscular  organization.  Every 
single  act  which  the  animal  is  capable  of  performing  has  its 
mechanism  provided  in  the  inherited  structure.  But  higher 
animals  may  learn  by  experience  to  combine  these  simple  ele- 
ments in  new  patterns.  The  higher  correlation  centers  serve  this 
function.  The  presence  arid  general  arrangement  of  these 
centers  is,  of  course,  also  determined  in  heredity;  but  the  partic- 


repfiles  birds 

Vertebrate     Phylum 

Fig.  4. — Two  diagrams  illustrating  the  relative  development  of  the 
invariable  and  variable  factors  in  the  behavior  of  the  articulate  phylum 
and  the  vertebrate  phylum  of  the  animal  kingdom.  In  the  articulate 
phylum  the  invariable  factor  (represented  by  the  shaded  area)  predominates 
throughout;  in  the  vertebrate  phylum  the  invariable  factor  predominates 
in  the  lower  members  of  the  series,  and  the  variable  factor  (represented  by 
the  unshaded  area)  increases  more  rapidly  in  the  higher  menibers,  attaining 
its  maximum  in  man,  where  intelligence  assumes  the  dominant  role. 

ular  associations  which  will  be  effected  within  them  are  deter- 
mined by  individual  experience,  and  the  builcUng  up  of  these 
new  associations  is  the  chief  business  of  education  (see  p.  312). 
In  the  analysis  of  behavior  and  the  related  neurological  mechan- 
isms the  distinction  between  the  innate  and  the  individually 
acquired  factors  must  always  be  kept  clearly  in  mind.  The 
failure  to  do  so,  and  also  the  failure  to  distinguish  between  these 


THE    NERVOUS    FUNCTIONS  35 

two  factors  and  the  acquired  automatisms  (p.  32),  is  responsible 
for  much  confusion  in  the  current  discussions  of  instinct. 

In  the  nomenclature  of  the  correlation  centers  thei-e  is  considerable 
diversity  of  usage.  In  describing  the  adjustments  made  by  these  centers 
neurologists  frequently  use  the  words  coordination,  correlation,  and  associ- 
ation in  about  the  same  sense;  but  the  adjustments  made  in  those  centers 
which  lie  closer  to  the  receptors  or  sense  organs  are  physiologically  of  dif- 
ferent type  from  those  made  in  the  centers  related  more  closely  to  the 
effector  apparatus.  In  recognition  of  this  fact  the  following  usage  has  been 
suggested  to  me  by  Dr.  F.  L.  Landacre  and  will  be  adopted  in  this  work: 

The  term  correlation  is  applied  to  those  combinations  of  the  afferent 
impulses  within  the  sensory  centers  which  provide  for  the  integration  of 
these  impulses  into  approi)riate  or  adaptive  responses;  in  other  words,  the 
correlation  centers  determine  what  the  reaction  to  a  given  combination  of 
stimuli  will  be.  Nervous  impulses  from  different  receptors  act  upon  the 
correlation  centers,  and  the  reaction  which  follows  will  be  the  resultant  of 
the  interaction  of  all  of  the  afferent  impulses  (and  physiological  traces  or 
vestiges  of  previous  similar  responses)  involved  in  the  process.  When  this 
resultant  nervous  discharge  passes  over  into  the  motor  centers  and  path- 
ways, the  final  common  paths  (see  p.  62)  innervated  will  lead  to  a  response 
whose  character  is  determined  by  the  organization  of  the  particular  motor 
centers  and  paths  actuated. 

To  the  term  coordination  we  shall  give  a  restricted  significance,  applying 
it  only  to  those  processes  employing  anatomically  fixed  arrangements  of  the 
motor  apparatus  which  provide  for  the  co-working  of  particular  groups  of 
muscles  (or  other  effectors)  for  the  performance  of  definite  adaptively  useful 
responses.  Every  reaction — even  the  simplest  reflex — involves  the  com- 
bined action  of  several  different  muscles,  and  these  muscles  are  so  inner- 
vated as  to  facilitate  their  concerted  action  in  this  particular  movement. 
These  are  called  sj^nergic  muscles.  Coordination  involves  those  adjust- 
ments which  are  made  on  the  effector  side  of  the  reflex  arc  (p.  56).  This 
is  the  sense  in  which  the  term  is  applied  by  Sherrington  in  the  foUowing 
passage  (Integrative  Action  of  the  Nervous  System,  p.  84): 

"Reflex  coordination  makes  separate  muscles  whose  contractions  act 
harmoniously,  e.  g.,  on  a  lever,  contract  together,  although  at  separate 
places,  so  that  they  assist  toward  the  same  end.  In  other  words,  it  excites 
synergic  muscles.  But  it  in  many  cases  does  more  than  that.  \ATiere  two 
muscles  would  antagonize  each  other's  action  the  reflex  arc,  instead  of 
activating  merely  one  of  the  two,  causes  when  it  activates  the  one  depression 
of  the  activity  (tonic  or  rhythmic  contraction)  of  the  other.  The  latter  is 
an  inhibitory  effect." 

The  motor  paths  and  centers  in  general  are  more  simply  organized  than 
are  the  sensory  paths  and  centers.  The  nervous  discharges  through  these 
motor  systems  are  very  direct  and  rapid.  Complex  nervous  reactions 
require  more  time  than  simple  reflexes,  and  this  delay  or  central  pause  is 
chiefly  in  the  correlation  centers  rather  than  in  the  efferent  coordination 
mechanisms  (see  pp.  9S,  181). 

The  word  association  may  be  reserved  for  those  higher  correlations 
where  plasticity  and  modifiability  are  the  dominant  features  of  the  response 
and  whose  centers  are  separated  from  the  peripheral  sensory  apparatus  by 
the  lower  correlation  centers  which  are  devoted  to  the  stereotj'ped  invari- 
able reflex  responses.     Correlation  may  be  mechanically  determined  by 


36  INTRODUCTION   TO   NEUROLOGY 

innate  structure,  or  there  may  be  some  small  measure  of  individual  modifi- 
ability,  but  when  the  modifiability  comes  to  be  the  dominant  characteristic, 
so  that  the  result  of  the  stimulus  cannot  be  readily  predicted  with  mechan- 
ical precision,  the  process  may  be  called  association.  The  intelligent  types 
of  reaction  and  all  higher  rational  processes  belong  here,  and  the  cerebral 
cortex  is  the  chief  apparatus  employed. 

The  boundaries  between  the  three  types  of  centers  just  distinguished 
are  not  always  sharply  drawn,  especially  in  their  simpler  forms,  though  in 
general  they  are  easily  distinguished.  The  mechanisms  of  coordination 
are  neurologically  simpler  than  those  of  correlation  and  association,  and  in 
general  they  are  developed  in  the  more  ventral  parts  of  the  brain  and 
spinal  cord,  that  is,  below  the  hmiting  sulcus  of  the  embryonic  brain  (p.  120). 
The  correlation  and  association  centers  are  developed  in  the  more  dorsal 
parts  of  the  brain  and  cord,  and  the  greater  part  of  the  thalamus  and  cere- 
bral hemispheres  is  composed  of  tissues  of  this  type.  Nevertheless,  the  dis- 
tinctions here  drawn  are  fundamentally  physiological  rather  than  anatom- 
ical, and  coordination  centers  may  be  developed  in  the  dorsal  parts  of  the 
brain,  as  in  the  case  of  the  cerebellum  and  probably  also  the  corpus  striatum 
of  mammals  (though  not  the  striatum  of  lower  vertebrates). 

Summary. — The  functions  which  characterize  the  nervous 
system  have  been  derived  from  those  of  ordinary  protoplasm 
by  further  development  of  three  of  the  fundamental  protoplas- 
mic properties — viz.,  sensitivity,  conductivity,  and  correlation. 
The  most  primitive  form  of  nervous  system  known  is  diffuse  and 
local  in  its  action,  but  in  all  the  more  highly  developed  forms  the 
chief  nervous  organs  tend  to  be  centralized  for  ease  of  general 
correlation  and  control.  Most  of  the  types  of  nervous  systems 
found  in  the  animal  kingdom  are  represented  in  two  distinct  and 
divergent  lines  of  evolution,  one  adapted  especially  well  for  the 
reflex  and  instinctive  mode  of  life  and  found  in  the  worms,  in- 
sects, and  their  allies,  and  the  other  found  in  the  vertebrates  and 
culminating  in  the  human  brain  with  its  remarkable  capacity 
for  individually  acquired  and  conscious  functions. 

Literature 

Barker,  L.  F.  1901.  The  Nervous  System  and  Its  Constituent  Neu- 
rones, New  York. 

Child,  C.  M.  1911.  The  Regulatory  Processes  in  Organisms,  Journal  of 
Morphology,  vol.  xxii,  pp.  171-222. 

Edinger,  L.  1908.  The  Relations  of  Comparative  Anatomy  to  Compar- 
ative Psychology,  Jour.  Comp.  Neur.,  vol.  xviii,  pp.  437-457. 

Herrick,  C.  Judson.  1910.  The  Evolution  of  Intelligence  and  Its 
Organs,  Science,  N.  S.,  vol.  xxxi,  pp.  7-18. 

— .  1910.  The  Relations  of  the  Central  and  Peripheral  Nervous  Systems 
in  Phylogeny,  Anat.  Record,  vol.  iv,  pp.  59-69. 


THE    NERVOUS    FUNCTIONS  37 

Jennings,  H.  S.  1905.  The  Method  of  Regulation  in  Behavior  and  in 
Other  Fields,  Jour.  Exp.  ZooL,  vol.  ii,  pp.  473-494. 

— .  1906.  Behavior  of  the  Lower  Organisms,  New  York. 

Lewandowsky,  M.  1907.  Die  Funktionen  des  zentralen  Nervensystems, 
Jena. 

LoEB,  J.  1900.  Comparative  Physiology  of  the  Brain  and  Comparative 
Psychology,  New  York. 

Parker,  G.  H.  1909.  The  Origin  of  the  Nervous  System  and  Its  Ap- 
propriation of  Effectors,  Pop.  Sci.  Monthly,  vol.  Ixxv,  pp.  56-64,  137-146, 
253-263,  338-345. 

— .  1914.  The  Origin  and  Evolution  of  the  Nervous  System,  Pop.  Sci. 
Monthly,  vol.  Ixxxiv,  pp.  118-127. 

Parmelee,  M.  1913.  The  Science  of  Human  Behavior,  New  York. 

Sherrington,  C.  S.  1906.  The  Integrative  Action  of  the  Nervous  Sys- 
tem, New  York. 

Yerworn,  M.  1899.  General  Physiology,  London. 

Washburn,  Margaret  F.  1908.  The  Animal  Mind,  New  York. 

Watson,  J.  B.  1914.  Behavior,  An  Introduction  to  Comparative  Psy- 
chology, New  York. 

Yerkes,  R.  M.  1905.  Concerning  the  Genetic  Relations  of  Types  of 
Action,  Jour.  Comp.  Neur.,  vol.  xv,  pp.  132-137. 


CHAPTER  III 

THE    NEURON 

As  we  have  seen  in  the  last  chapter,  the  functions  of  irrita- 
bihty,  conduction,  and  correlation  are  the  most  distinctive  fea- 
tures of  the  nervous  system.  Like  the  rest  of  the  body,  the 
nervous  tissues  are  composed  of  cells,  the  irritability  of  whose 
protoplasm  is  of  diverse  sorts  in  adaptation  to  different  func- 
tional requirements.  Each  sense  organ,  for  instance,  is  irri- 
table to  its  own  adequate  stimulus  only  (see  pp.  25,  69).  The 
functions  of  correlation  and  integration  of  bodily  actions  cannot 
be  carried  on  by  the  nerve-cells  as  individuals,  but  they  are 
effected  by  various  types  of  connections  between  the  different 
cells  in  the  nerve-centers.  The  character  of  any  particular  cor- 
relation, in  other  words,  is  a  function  of  the  pattern  in  accord- 
ance with  which  the  nerve-cells  concerned  are  connected  with 
each  other  and  with  the  end-organs  of  the  reflex  arcs  involved. 
The  conducting  function  of  nerve-cells  is,  perhaps,  their  most 
striking  peculiarity,  and  their  very  special  forms  are  due  largely 
to  the  fact  that  their  business  is  to  connect  remote  parts  of  the 
body  so  that  these  parts  can  cooperate  in  complicated  move- 
ments. 

Not  all  of  the  cells  which  compose  the  central  nervous  system  are  nerve- 
cells.  The  brain  and  spinal  cord  are  surrounded  by  three  connective-tissue 
membranes  (dura  mater,  arachnoid,  and  pia  mater,  in  the  aggregate 
termed  meninges)  whose  functions  are  chiefly  protective  and  nutritive; 
from  the  inner  membrane,  the  pia  mater,  blood-vessels,  and  strands  of 
connective  tissue  extend  into  the  true  nervous  substance.  In  addition  to 
these  non-nervous  elements  which  grow  into  the  central  nervous  system 
from  without,  the  substance  of  the  brain  and  spinal  cord  contains  a  sup- 
porting framework  composed  of  ependyma  and  neuroglia  or  glia  cells  which 
develop  from  the  primitive  embryonic  nervous  system  (the  neural  tube,  see 
pp.  106,  116),  but  are  not  known  to  perform  nervous  functions,  though 
nutritive  and  other  functions  have  been  ascribed  to  them  (see  p.  104). 

The  true  nerve-cells  are  called  neurons.  There  has  been  a 
long  controversy  regarding  the  way  in  which  the  neurons  of  the 

38 


THE    NEURON  39 

adult  body  are  developed  from  the  cells  of  the  embryonic  nervous 
system;  but  it  is  now  generally  accepted  that  each  neuron  is 
developed  from  a  single  embryonic  cell  (known  as  a  neurol^last), 
and  that  in  the  adult  body  each  neuron  has  a  certain  measure  of 
anatomical  and  physiological  distinctness  from  all  of  the  others. 

The  very  young  nerve-cell  (neuroblast)  is  oval  in  form  and  is 
composed  of  a  nucleus  and  its  surrounding  protoplasm  (cyto- 
plasm); but  in  further  development  it  rapidly  elongates  by  the 
outgrowth  of  one  or  more  fibrous  processes  from  the  cell  body, 
so  that  the  mature  neuron  may  be  regarded  as  a  protoplasmic 
fiber  with  a  thickening  somewhere  in  its  course  which  is  the  cell 
body  of  the  original  neuroblast  and  contains  the  cell  nucleus 
and  a  part  only  of  its  cytoplasm  (this  part  being  called  the 
perikaryon),  the  remainder  of  the  cytoplasm  composing  the 
fibrous  processes,  that  is,  the  nerve-fibers.  The  cell  body  of 
the  mature  neuron  is  sometimes  loosely  termed  the  nerve-cell, 
though  the  latter  term  should  strictly  include  the  entire  neuron. 
The  importance  of  the  conducting  function  is  reflected  in  the  elon- 
gated forms  of  the  neurons  and  in  the  peculiar  protoplasmic  struc- 
ture of  the  nerve-fibers.  The  function  of  the  cell  body  is  chiefly 
nutritive;  the  entire  neuron  dies  if  the  cell  body  is  destroyed. 

Each  neuron  may  be  regarded  as  essentially  an  elongated  con- 
ductor, and  these  units  are  arranged  in  chains  in  such  a  way  that 
a  nervous  impulse  is  passed  from  one  to  another  in  series.  Since 
the  arrangement  is  such  that  the  nervous  impulse  usually 
passes  through  the  series  in  only  one  direction  (see  the  typical 
reflex  arc.  Fig.  1,  p.  25),  each  neuron  has  a  receptive  function 
at  one  end  and  discharges  its  impulse  at  the  other  end.  This  is 
what  is  meant  by  the  polarity  of  the  neuron  (see  pp.  52  and  97). 

The  simpler  forms  of  neurons  are  bipolar,  with  one  or  more 
processes  known  as  dendrites  conducting  nervous  impulses  toward 
the  cell  body,  and  (usually)  only  one  process,  the  axon  or  neurite, 
conducting  away  from  the  cell  body.  The  dendrites  are  usually 
short,  and  in  this  case  their  structure  is  similar  to  that  of  the  cell 
body.  But  where  the  dendrites  are  long,  as  in  the  neurons  of  the 
spinal  and  cranial  ganglia  (Figs.  1,  10),  they  may  have  the 
same  structure  as  the  axon.  The  axons  are  the  axis-cylinders 
of  the  longer  nerve-fibers  and  are  structurally  very  different  from 
the  protoplasm  of  the  cell  body,  being  composed  chiefly  of 


40 


INTRODUCTION  TO  NEUROLOGY 


numerous  very  delicate   longitudinally  arranged  neurofibrillse 
embedded  in  a  small  amount  of  more  fluid  protoplasm. 


Fig.  5. — Diagram  of  a  motor  neuron  from  the  ventral  column  of  gray 
matter  in  the  spinal  cord.  The  cell  body,  dendrites,  axon,  collateral 
branches,  and  terminal  arborizations  in  muscle  are  all  seen  to  be  parts  of  a 
single  cell  and  together  constitute  the  neuron:  ah,  Axon  hiUock  free  from 
chromophilic  bodies;  ax,  axon;  c,  cytoplasm  of  cell  body  containing  chromo- 
philic  bodies,  neurofibrils,  and  other  constituents  of  protoplasm;  d,  den- 
drites; m,  myelin  (medullary)  sheath;  m',  striated  muscle-fiber;  n,  nucleus; 
n',  nucleolus;  nR,  node  of  Ranvier  where  the  axon  divides;  sf,  collateral 
branch;  si,  neurilemma  (not  apart  of  the  neuron);  tel,  motor  end-plate. 
(After  Barker,  from  Bailey's  Histology.) 

The  forms  of  neurons  are  infinitely  diverse  and  appear  to  have 
been  determined  by  two  chief  factors;  these  are  (1)  the  nutrition 


THE    NEURON 


41 


of  the  cell  and  (2)  the  specific  functions  of  conduction  to  be 
served.  The  dendrites  spread  widely  throughout  the  surround- 
ing tissues,  thus  giving  the  cell  a  large  surface  for  the  rapid  ab- 
sorption of  food  materials  from  the  surrounding  lymph.  This 
was  regarded  as  the  only  function  of  the  dendrites  by  Golgi  and 
some  of  the  other  pioneers  in  the  study  of  neurons,  and  led  them 
to  apply  the  name  "protoplasmic  processes"  to  these  structures. 
We  have  already  seen  that  the  dendrites  are  more  than  this, 


Fig.  6. — Enlarged  view  of  a  cell  body  similar  to  that  of  Fig.  5,  from  the 
spinal  cord  of  an  ox,  showing  the  large  chromophilic  bodies:  a,  Pigment; 
h,  axon;  c,  axon  hillock;  d,  dendrites.     (After  von  Lenhossek.) 


however,  being  the  usual  avenues  by  which  nervous  impulses 
enter  the  cell  body.  The  size,  length,  and  mode  of  branching 
of  the  dendrites  are,  therefore,  chiefly  determined  by  their  rela- 
tions to  other  neurons  from  which  they  receive  their  nervous 
impulses.  The  axon  probably  plays  but  little  part  in  the  gen- 
eral nutrition  of  the  cell,  and  its  form  is  shaped  almost  entirely 
by  the  distance  to  be  traversed  in  order  to  reach  the  center  or 
centers  into  which  it  discharges. 


42 


INTRODUCTION   TO    NEUROLOGY 


Neurons  can  function  only  when  connected  together  in  chains, 
so  that  the  nervous  impulse  can  be  passed  from  one  to  the  other. 
In  any  such  chain  the  neuron  first  to  be  excited  is  called  the 
neuron  of  the  first  order,  and  the  succeeding  members  of  the 
series  neurons  of  the  second,  third,  fourth  order,  and  so  forth. 
All  reflexes  require  an  afferent  neuron  which  conducts  the  ner- 
vous impulse  from  the  receptor  to  the  center,  one  or  more  effer- 
ent neurons  conducting  from  the  center  to  the  organ  of  response, 


Fig.  7. — The  body  of  a  pjTamidal  neuron  from  the  cerebral  cortex, 
stained  by  Nissl's  method,  illustrating  the  arrangement  of  the  chromophilic 
substance  and  the  form  of  the  nucleus:  a,  Axon;  h,  chromophilic  bodies 
surrounding  the  nucleus;  c,  a  mass  of  chromophilic  substance  in  the  angle 
formed  by  the  branching  of  a  dendrite;  d,  nucleus  of  a  neuroglia  cell  (not  a 
part  of  the  neuron).     (After  Ramon  y  Cajal.) 

and  usually  one  or  more  neurons  intercalated  between  these 
within  the  center  itself  (see  pp.  25,  56,  109).  Figure  1,  p.  25, 
illustrates  the  simplest  possible  connection  of  neurons  in  a  reflex 
arc  of  the  spinal  cord,  involving  only  two  elements.  The 
afferent  neuron  sends  its  dendrite  to  the  skin  and  its  axon  into 
the  spinal  cord,  where  the  nervous  impulse  is  taken  up  by  the 
dendrites  of  the  efferent  neuron,  which  in  turn  transmits  it  to  a 
muscle.     Figures  5  to  9  illustrate  the  forms  of  other  neurons. 


THE    NEURON  43 

The  different  dendrites  of  a  neuron  may  be  physiologically 
all  alike,  or  they  may  spread  out  in  different  directions  to  receive 
nervous  impulses  of  diverse  sorts  from  different  sources.  Simi- 
larly the  axon  may  discharge  its  nervous  impulse  into  a  single 
nerve  center  or  peripheral  end-organ,  or  it  may  branch,  thus 
connecting  with  and  stimulating  to  activity  two  or  more  diverse 
functional  mechanisms.  In  other  words,  a  given  neuron  may  be 
a  link  in  a  chain  of  some  simple  nervous  circuit  (Fig.  1),  or  it 
may  be  adapted  to  collect  nervous  impulses  from  different 
sources  and  discharge  them  into  a  single  final  common  path,  or 
in  the  third  place  it  may  receive  nervous  impulses  of  one  or  more 
functional  sorts  and  then  discharge  its  own  nervous  energy  into 
several  remote  parts  of  the  nervous  system.  This,  in  brief,  is  the 
mechanism  of  correlation,  and  illustrations  of  these  different 
types  of  connection  will  be  found  in  the  following  chapters.  If 
animal  reactions  were  simple  responses  so  arranged  that  a  given 
stimulus  could  produce  only  one  kind  of  movement,  the  only 
nervous  mechanism  required  would  be  a  single  neuron  transmit- 
ting the  excitation  from  the  point  of  stimulation  to  the  organ  of 
response,  as  a  call  bell  may  be  rung  by  pulling  a  bell  cord.  But 
the  actual  reactions  are  always  more  complex  than  this,  so  that 
several  neurons  must  be  connected  in  series  with  various  di- 
vergent pathways  of  nervous  discharge  which  reach  different 
correlation  centers,  all  of  which  must  cooperate  in  the  final 
response.  Illustrations  of  some  of  these  complicated  reflex 
mechanisms  will  be  found  in  Chapter  IV. 

Neurons  with  short  dendrites  and  a  single  long  axon  are  the 
most  common  form  and  were  termed  Type  I  by  Golgi  (Fig.  8). 
In  some  cases  (Fig.  9)  the  axon  also  is  very  short,  breaking  up 
in  the  immediate  neighborhood  of  the  cell  body;  these  are  the 
Type  II  neurons  of  Golgi  and  appear  to  be  adapted  for  the  dift'u- 
sion  and  summation  of  stimuli  within  a  nerve  center.  The 
neurons  of  the  spinal  and  cranial  ganglia  form  a  third  type. 
In  embryonic  development  the}^  begin  as  bipolar  cells  with  a 
dendritic  process  at  one  end  and  an  axonal  process  at  the 
opposite  end  of  the  cell  body;  but  in  the  course  of  further  devel- 
opment (Fig.  10)  the  two  processes  approach  each  other  and 
finally  unite  for  a  short  distance  into  a  single  stem,  which  then 
separates  into  an  axon  and  a  highl}^  special  form  of  dendrite 


44 


INTRODUCTION  TO   NEUROLOGY 


Fig.  9. — Neuron  of  Type  II  from 
the  cerebral  cortex  of  a  cat.  The 
entire  neuron  is  included  in  the 
drawing:  a,  Axon  which  branches 
freely  and  terminates  close  to  the 
cell  body;  d,  dendrites.  (After 
Kolliker.) 


Fig.  8. — Pyramidal  neuron  (Type 
I  of  Golgi)  from  the  cerebral  cortex 
of  a  rabbit.  The  axon  gives  off 
numerous  collateral  branches  close 
to  the  cell  body  and  then  enters  the 
white  substance,  within  which  it  ex- 
tends for  a  long  distance.  Only  a 
small  part  of  the  axon  is  included  in 
the  drawing :  a,  Axon ;  b,  white  sub- 
stance; c,  collateral  branches  of 
axon;  d,  chief  dendrite;  p,  its  ter- 
minal branches  at  the  outer  surface 
of  brain.     (After  Ramon  y  Cajal.) 


which  has  the  same  microscopic  structure  as  the  axon,  but  con- 
ducts in  the  opposite  direction  with  reference  to  the  cell  body. 
This  produces  a  T-form  unipolar  cell.     The  axon  usually  arises 


THE    NEURON 


45 


from  the  cell  body;  it  may  arise  from  the  base  of  one  of  the  den- 
drites or,  rarely,  from  the  apex  of  the  chief  dendrite  (Fig.  11). 

Neurons  differ  in  internal  structure,  as  well  as  in  form,  from 
the  other  cells  of  the  body.     The  most  important  of  these  pecu- 


Fig.  10. — A  collection  of  ceUs  from  the  ganglion  of  the  trigeminus  of  the 
embryonic  guinea-pig,  to  illustrate  various  stages  in  the  transformation  of 
bipolar  neuroblasts  into  unipolar  ganglion  cells.     (After  Van  Gehuchten.) 


liarities  are,  first,  the  fibrillar  structure  of  their  cytoplasm, 
and,  second,  the  presence  in  the  cytoplasm  of  a  highly  complex 
protein  substance  chemically  alhed  to  the  chromatin,  which  is 


Fig.  11. — A  neuron  from  the  primary  gustatory  center  in  the  medulla 
oblongata  of  the  carp.  (Figure  136  (2),  p.  303,  illustrates  the  enormous 
enlargement  of  the  medulla  oblongata  of  this  fish  which  is  produced  by  this 
gustatory  center.)  The  peripheral  gustatory  nerves  end  among  the 
dendrites,  d.  The  axis  of  the  main  dendrite  is  directly  prolonged  to  form 
the  axon,  a.  The  heavy  line  at  the  right  marks  the  external  surface  of  the 
brain.     (From  the  Journal  of  Comparative  Neurology,  vol.  xv,  p.  395.) 

the  best  known  and  probably  the  most  important  constituent  of 
the  cell  nucleus.  This  is  the  chromophiUc  substance,  which  in 
nerve-cells  as  seen  under  the  microscope  is  ordinarily  arranged 
in  more  or  less  definite  flake-like  masses  scattered  throughout 


46  INTRODUCTION  TO  NEUROLOGY 

the  cytoplasm  of  the  cell  and  extending  out  into  the  larger  den- 
drites (see  Figs.  6,  7).  These  masses  were  first  carefully  investi- 
gated by  Nissl,  who  devised  a  special  staining  method  for  that 
purpose;  they  are,  accordingly,  often  called  the  Nissl  bodies,  and 
sometimes  tigroid  bodies.  They  never  occur  in  the  axon  nor 
in  a  special  conical  protuberance  of  the  cell  body  (the  axon 
hillock)  from  which  the  axon  arises  (see  Fig.  5,  ah,  and  Fig.  6,  c). 

The  neurofibrils  are  very  delicate  strands  of  denser  protoplasm 
found  in  all  parts  of  the  neuron  except  the  nucleus.  They  are  by 
many  regarded  as  the  specific  conducting  elements  of  the  neuron, 
though  the  evidence  for  this  is  not  conclusive.  They  ramify 
throughout  the  cytoplasm  (Fig.  12),  passing  through  the  cell 
body  from  one  process  to  another. 

The  longer  nerve-fibers  are  usually  enveloped  by  a  thick  white 
glistening  sheath  of  myehn,  a  fat-like  substance  secreted  by  the 
nerve-fibers  themselves.  This  myelin  sheath,  or  medullary 
sheath,  is  a  part  of  the  neuron  with  which  it  is  related  and  the 
fibers  which  possess  it  are  called  myelinated  or  medullated  fibers; 
these  fibers  compose  the  white  matter  of  the  brain  and  a  large 
part  of  the  peripheral  nerves  (see  Fig.  5).  There  may  be,  in  ad- 
dition, in  the  case  of  the  peripheral  nerves  an  outer  sheath,  the 
neurilemma  (primitive  sheath  or  sheath  of  Schwann).  This  is  a 
thinner  nucleated  membrane,  not  a  part  of  the  neuron  to  which 
it  is  attached,  but  formed  from  surrounding  cells. 

The  function  of  the  myelin  sheath  has  often  been  regarded  as 
simply  that  of  an  insulating  substance  to  prevent  the  overflow 
and  loss  of  the  nervous  impulse  conducted  by  the  axon,  but 
there  is  some  evidence  that  this  sheath  plays  an  important  part 
in  the  chemical  processes  involved  in  the  act  of  nervous  conduc- 
tion. The  neurilemma  is  likewise  often  spoken  of  as  a  protecting 
membrane.  Whether  it  has  any  other  function  in  the  normal 
life  of  the  nerve-fiber  is  unknown;  but  if  a  nerve-fiber  is  by  acci- 
dent severed  from  its  cell  body,  it  is  known  that  the  nuclei  of 
the  neurilemma  play  a  very  important  part  in  the  degeneration 
and  regeneration  of  the  severed  fiber  and  the  restoration  of  its 
normal  function. 

As  has  been  suggested,  nerve-fibers  cut  off  from  their  cell 
bodies  immediately  die  and  degenerate.  But  in  the  case  of 
peripheral  nerves  the  neurilemma  nuclei  do  not  die;  and,  appa- 


THE   NEURON 


47 


rently  with  the  aid  of  these  nuclei,  a  new  nerve-fiber  may  under 
favorable  conditions  grow  out  from  the  central  stump  of  the  cut 
nerve,  and  finally  the  entire  nerve  may  regenerate.     In  the  cen- 


Fig.  12. — Cell  from  the  ventral  gray  column  of  the  human  spinal  cord, 
illustrating  the  arrangement  of  the  neurofibrils:  ax,  Axon;  lu,  interfibril- 
lar  spaces  occupied  by  chromophilic  substance;  n,  nucleus;  x,  neurofibrils 
passing  from  one  dendrite  to  another;  y,  similar  neurofibrils  passing  through 
the  body  of  the  cell.    (After  Bethe,  from  Heidenhain's  Plasma  und  Zelle). 


tral  nervous  system,  where  the  neurilemma  is  absent  or  greatly 
reduced,  the  regeneration  of  such  injured  nerves  takes  place 
with  great  difficulty,  if  at  all. 


48 


INTRODUCTION   TO   NEUROLOGY 


It  is  possible  by  a  special  method  of  staining  devised  by  Marchi 
to  differentiate  myelinated  fibers  which  are  in  process  of  degen- 
eration from  the  normal  fibers  with  which  they  may  be  mingled. 
This  method  has  often  permitted  a  much  more  precise  deter- 
mination of  the  exact  course  of  the  fibers  of  a  given  peripheral 


Fig.  13. — Two  motor  neurons  from  the  ventral  column  of  gray  matter  of 
the  spinal  cord  of  a  rabbit,  taken  fifteen  days  after  cutting  the  sciatic  nerve, 
to  illustrate  the  chromatolysis  of  the  chromophilic  substance:  A,  Cell  in 
which  the  chromophilic  bodies  are  partially  disintegrated  (at  b)  and  the 
nucleus  eccentric;  B,  cell  showing  more  advanced  chromatolysis  (c),  the 
chromophilic  substance  being  present  only  in  the  dendrites  and  around  the 
nucleus  in  the  form  of  a  homogeneous  mass;  a,  axon.  Compare  with  these 
appearances  the  normal  cell  of  the  ventral  column  shown  in  Fig.  6.  (After 
Ramon  y  Cajal.) 

nerve  or  central  tract  than  would  be  possible  by  the  examination 
of  normal  material,  especially  after  experimental  operations  on 
the  lower  animals,  where  the  particular  collection  of  fibers  under 
investigation  may  be  severed  and  then  later  the  animal  killed 
and  examined  by  Marchi's  method  (see  p.  135). 

It  is  also  found  that  after  cutting  any  group  of  nerve-fibers  the 


THE    NEURON  49 

cell  bodies  from  which  these  fibers  arise  show  structural  changes. 
The  most  important  change  is  a  solution  of  the  chromophilic 
substance  or  Nissl  bodies  so  that  they  no  longer  appear  in  a 
stained  preparation  (Fig.  13).  This  is  termed  chromatolysis, 
and  often  enables  the  neurologist  to  determine  exactly  which 
cells  in  the  central  nervous  system  give  rise  to  a  particular 
bundle  of  fibers  (for  examples  see  pp.  136  and  284) . 

The  neuron  doctrine  may  be  said  to  date  from  the  publica- 
tion of  important  papers  by  Golgi,  of  Pavia,  in  1882  to  1885 
(though  his  now  famous  method  was  published  in  1873,  and 
many  of  Golgi's  theoretical  conclusions  have  been  greatly 
modified).  The  name  Neuron  (in  English  often  spelled 
"neurone")  was  first  applied  by  Waldeyer  in  1891  in  connection 
with  a  clear  enunciation  of  the  recently  demonstrated  facts  upon 
which  the  concept  is  based.  The  discovery  of  William  His 
that  the  nervous  system  is  made  up  of  cellular  units  which  are 
embrj^ologically  distinct,  and  the  further  demonstration  by 
others  that  these  cellular  elements  retain  some  measure  of  ana- 
tomical and  physiological  individuality  (the  exact  degree  of 
anatomical  separation  is  still  in  controversy — some  say  it  is  com- 
plete) up  to  adult  life  revolutionized  neurology,  and  this  doctrine 
has  profoundly  influenced  all  subsequent  neurological  work.  The 
histor}^  of  this  movement  we  cannot  here  go  into  (see  the  excel- 
lent summaries  in  Barker's  Nervous  System  and  the  article  by 
Adolf  Meyer  cited  at  the  end  of  this  chapter).  The  present 
status  of  the  neuron  doctrine  has  been  summarized  by  Heiden- 
hain  (1911,  p.  711)  in  the  following  six  propositions: 

1.  The  neuron  of  the  adult  animal  body  is  an  anatomical  unit; 
it  corresponds  morphologically  to  one  cell. 

2.  The  neuron  is,  accordingl}^,  also  a  genetic  unit,  for  it  is 
differentiated  from  a  single  embryonic  cell. 

3.  Nervous  substance  is  composed  of  the  contained  neurons; 
within  the  nervous  sj^stem  there  are  no  elements  other  than 
neurons  which  participate  in  nervous  functions. 

4.  The  neurons  remain  anatomically  separate;  they  are  merety 
in  contact  with  each  other,  that  is,  there  are  no  connections 
between  them  which  are  characterized  as  conditions  of  conti- 
nuity or  fusion  of  their  substance. 

5.  The  neuron  is  a  trophic  unit.     This  means  that  the  injur}' 

4 


50 


INTRODUCTION   TO   NEUROLOGY 


of  any  part  of  the  neuron  affects  the  welfare  of  the  whole,  and 
the  destruction  of  the  nucleus  and  cell  body  destroys  the  entire 
neuron,  but  such  injuries  do  not  directly  affect  adjacent 
neurons. 

6.  The  neuron  is  a  functional  unit  or,  better,  the  functional 
unit  of  the  nervous  system. 


Fig.  14. — Neurons  from  the  trapezoid  body  of  the  medulla  oblongata  of  a 
cat,  illustrating  different  forms  of  synapse:  a,  Delicate  pericellular  net 
around  the  cell  body  of  a  neuron  which  is  not  shown;  b,  coarser  endings;  c, 
still  coarser  net;  d,  calyx-like  envelope.  In  b,  c,  and  d,  at  the  left  of  the 
figure,  the  globular  cell  body  of  the  neuron  of  the  second  order  is  shaded 
with  lighter  stipple  than  the  terminals  of  the  axon  of  the  neuron  of  the  first 
order.  (After  Veratti,  from  Edinger's  Vorlesungen.)  (It  should  be  noted 
that  in  this  account  we  do  not  follow  Veratti's  interpretation  of  these 
structures,  but  that  of  Held,  Ramon  y  Cajal,  and  the  majority  of  other 
neurologists.) 

These  six  propositions  are  accepted  in  their  entirety  by  many 
neurologists;  but  it  should  be  clearly  understood  that  all  of 
them  are  controverted  by  others.  The  fourth  proposition,  in 
particular,  has  been  the  subject  of  violent  attack  (see  the  dis- 
cussion of  the  synapse  below).  The  neuron,  moreover,  is  a 
functional  unit  (proposition  6)  in  only  a  rather  limited  sense 
(see  p.  56).     Without  further  discussion  of  the  merits  of  these 


THE    NEURON 


51 


controversial  questions,  it  may  be  regarded  as  generally  accepted 
that  all  of  the  preceding  propositions  have  some  measure  of 
factual  basis,  though  different  neurologists  would  give  various 
interpretations  and  modifications  of  some  of  them. 

The  place  where  the  axon  of  one  neuron  comes  into  physio- 
logical relation  with  another  neuron  is  known  as  the  synapse. 


Fig.  15. — Synapse  between  an  ascending  fiber  entering  the  cortex 
of  the  cerebellum  and  the  dendrites  of  a  Pur  kin  je  cell.  (After  Ramon  y 
Cajal.) 


Its  precise  nature  is  still  obscure.  Structurally  it  usually  ex- 
hibits a  dense  interlacing  of  the  terminal  arborization  of  an  axon 
of  one  neuron  with  the  bushy  dendrite  of  a  second  neuron. 
In  Fig.  1  (p.  25)  such  a  synapse  is  seen  between  the  dorsal  root 
neuron  and  the  ventral  root  neuron.  In  other  cases  the  ter- 
minal arborization  takes  the  form  of  a  delicate  network  which 


52 


INTRODUCTION  TO  NEUROLOGY 


twines  around  the  cell  body  of  the  second  neuron  or  of  a  calyx- 
like expansion  or  coarse-meshed  reticulum  closely  enveloping 
the  cell  body  (Fig.  14).  Another  form  of  synapse  is  seen  in  Fig. 
15  from  the  cortex  of  the  cerebellum.  The  body  and  larger 
dendrites  of  a  single  cortical  neuron  of  the  type  known  as 
Purkinje  cells  (see  p.  191)  are  shown  in  gray,  and  the  terminal 
branches  of  an  afferent  neuron  are  seen  twining  about  the  den- 
dritic branches  of  the  Purkinje  cell,  thus  forming  a  very  intimate 
union.  Similar  synapses  are  found  in  the  cerebral  cortex  (p. 
272).    Figure  16  illustrates  a  type  of  synapse  also  found  in  the 


Fig.  16. — A  "basket  cell"  from  the  cerebellar  cortex  of  a  rat,  illustrating 
the  discharge  of  a  single  neuron,  B,  by  synaptic  connection  with  the  cell 
bodies  of  several  Purkinje  neurons,  A,  by  basket-like  endings  of  the  axon: 
A,  cells  of  Purkinje;  a,  the  basket-like  synapse  on  the  body  of  a  Purkinje 
cell;  B,  the  basket  cell;  h,  terminus  of  the  axon;  c,  axon  of  basket  cell. 
(After  Ramon  y  Cajal;  cf.  Fig.  89,  p.  190.) 


cerebellar  cortex.  A  single  "basket  cell,"  B,  has  a  short  axon 
whose  branches  form  synapses  around  the  bodies  of  a  large 
number  of  Purkinje  cells,  thus  diffusing  and  greatly  strength- 
ening the  nervous  discharge  (see  p.  192  and  Fig.  89,  h).  For 
still  other  types  of  synapse  see  Figs.  61,  89,  98,  104,  109,  126. 
The  synapse  has  been  a  crucial  point  in  recent  discussions 
regarding  the  general  physiology  of  the  nervous  system,  many 
neurologists  believing  that  it  is  the  most  important  part  of  the 
reflex  circuits  (see,  for  instance,  on  the  theory  of  sleep,  p.  103). 
The  doctrine  of  the  polarization  of  the  neuron  (p.  39)  implies 


THE    NEURON 


53 


that  at  the  synapse  there  must  be  a  reversal  of  the  polarity  with 
reference  to  the  cell  body  as  the  nervous  impulse  passes  over 
from  an  axon  to  a  dendrite. 

In  the  simple  diffuse  form  of  nervous  system  found  in  primi- 
tive animals  like  the  jelly-fishes  and  lowest  worms  (p.  27)  the 
nerve-cells  are  described  as  connected  by  protoplasmic  strands 
to  form  a  continuous  network.     Here,  of  course,  there  are  no 


Fig.  17. — Plexus  of  sympathetic  neurons  in  the  villi  of  the  small  intes- 
tine of  a  guinea-pig:  a,  b,  c,  d,  Neurons  of  the  subepithelial  plexus;  e,  f, 
neurons  of  the  plexus  within  the  villi;  g,  fibers  of  the  submucous  (Meissner's) 
plexus.     (After  Ramon  y  Cajal.) 


synapses  and  the  neurons  are  not  polarized.  Apparent!}^  the 
nervous  impulse  may  be  transmitted  equally  well  in  all  direc- 
tions throughout  this  network.  The  physiological  properties 
of  such  an  arrangement  appear  to  be  very  different  from  those 
of  the  synaptic  nervous  systems  of  higher  animals.  A  non- 
synaptic  network  similar  to  that  mentioned  above  has.  been  des- 
cribed as  occurring  in  some  of  the  diffuse  ganglionic  plexuses  of 
the  human  body  (Fig.  1.7). 


54  INTRODUCTION  TO  NEUROLOGY 

In  the  synaptic  systems,  as  found  in  all  highly  differentiated 
nervous  centers,  the  majority  of  neurologists  teach  that  at  the 
synapse  the  two  neurons  involved  are  simply  in  contact  and  that 
the  nervous  impulse  passes  from  one  to  the  other  across  a  very 
short  gap  in  the  conducting  substance.  Others  believe  that 
they  have  demonstrated  very  delicate  protoplasmic  threads 
which  bridge  this  gap,  thus  establishing  continuity  of  the  con- 
ducting substance  across  the  synapse.  Good  histological  prepara- 
tions show,  however,  in  some  of  the  most  intimate  synapses 
known  where  the  axon  ends  directly  on  the  cell  body  of  the  sec- 
ond neuron  that  there  is  a  distinct  cellular  membrane  around 
the  terminals  of  the  fibers  of  the  first  order  and  a  second  cellu- 
lar membrane  enveloping  the  body  of  the  neuron  of  the  second 
order,  so  that  continuity  of  the  ordinary  protoplasm  of  the 
neurons  here  seems  to  be  quite  impossible,  so  far  as  our  present 
technic  is  adequate  to  decide  the  question.^ 

The  following  important  points  regarding  the  synapse  seem 
to  be  established: 

1.  Unimpeded  protoplasmic  continuity  across  the  synapse  has 
not  been  clearly  established,  and  in  some  cases  there  is  clearly 
a  membranous  barrier  interposed  between  the  two  neurons. 
But  the  exact  nature  of  this  barrier  is  unknown  and  it  by  no 
means  follows  that  the  synaptic  membrane  is  an  inert  substance. 
It  may  be  composed  of  living  substance  of  a  different  nature 
from  that  of  the  other  protoplasm  of  the  neurons; 

2.  The  transmission  of  the  nervous  impulse  across  the  synapse 
involves  a  delay  greater  than  that  found  in  the  nerve-fiber  or 
the  cell  body.  This  suggests  that  there  is  some  sort  of  an  ob- 
struction here  which  does  not  occur  elsewhere  in  the  reflex  arc 
(see  p.  98). 

3.  The  synapse  is  more  susceptible  to  certain  toxic  substances, 
such  as  nicotin,  than  is  any  other  part  of  the  reflex  arc. 

4.  Though  a  nerve-fiber  seems  to  be  capable  of  transmitting 
an  impulse  in  either  direction,  the  nervous  impulse  can  pass  the 
synapse  only  in  one  direction,  viz.,  the  direction  of  normal  dis- 
charge from  the  axon  of  one  neuron  to  the  dendrite  of  another. 

1  For  an  illustration  of  such  a  synapse  see  Bartlemez,  G.  W.,  Mauthner's 
Cell  and  the  Nucleus  Motorius  Tegmenti,  Jour.  Comp.  Neur.,  vol.  xxv, 
1915,  Figs.  11,  12,  and  13,  pp.  126-128. 


THE    NEURON  55 

The  synapse,  therefore,  acts  as  a  sort  of  valve,  to  use  a  crude 
analogy,  and  appears  to  be  one  of  the  factors  (not  necessarily 
the  only  one,  see  p.  97)  in  establishing  the  polarity  of  the  neuron. 

5.  Observations  upon  injured  neurons  show  that  the  degenera- 
tions caused  by  the  severance  of  their  fibrous  processes  (whether 
these  be  manifested  as  degeneration  of  the  fibers  or  as  chroma- 
tolysis,  see  p.  49)  or  by  the  destruction  of  the  cell  bodies  from 
which  the  fibers  arise  cannot  cross  the  barriers  interposed  by  the 
synapses. 

Summary. — In  this  chapter  the  form  and  internal  structure  of 
neurons  have  been  briefly  reviewed  and  the  present  status  of  the 
neuron  doctrine  is  summarized  on  p.  49.  The  synapse  is  the 
place  where  the  nervous  impulse  is  transmitted  from  one  neuron 
to  another,  and  it  is  regarded  as  of  the  utmost  physiological 
importance,  its  most  important  features  being  presented  briefly 
on  p.  54.  The  doctrine  of  the  polarization  of  the  neuron  teaches 
that  nervous  impulses  are  received  by  the  dendritic  processes 
and  transmitted  outward  from  the  cell  body  through  the  axon. 

Literature 

Apathy,  S.  1898.  Ueber  Neurofibrillen,  Proc.  Internat.  Zoological 
Congress,  Cambridge,  pp.  125-141. 

Barker,  L.  F.  1901.  The  Nervous  System  and  Its  Constituent  Neurones, 
New  York. 

Bethe,  a.  1904.  Der  heutige  Stand  der  Neurontheorie,  Deutsch. 
med.  Woch.,  No.  33. 

GoLGi,  C.  1882-1885.  Sulla  fina  anatomia  degli  organi  central!  del 
sistema  nervoso,  Riv.  Sperim.  di  Freniatria,  vols,  viii,  ix,  and  xi. 

— .  1907.  La  dottrina  del  neurone,  Teoria  e  fatti,  Arch.  Fisiol.,  vol.  iv, 
pp.  187-215. 

Heidenhain,  M.  1911.  Plasma  und  Zolle,  2  Lieferung  (in  Bardelcben's 
Handbuch  der  Anatomie  des  Menschen,  Bd.  8),  Jena. 

His,  W.  1889.  Die  Neiiroblasten  und  deren  Entstehung  im  embry- 
onalen  Mark,  Leipzig. 

Meyer,  Adolf.  1898.  Critical  Review  of  the  Data  and  General  Meth- 
ods and  Deductions  of  Modern  Neurology,  Jour.  Comp.  Neur.,  vol.  viii, 
pp.  11.3-148  and  249-313. 

NissL,  F.    1903.   Die  Neuronenlehre  und  ihre  Anhiinger,  Jena. 

Ram6n  y  Cajal,  S.  1909.  Histologie  de  Systeme  Nerveux,  Paris. 

Waldeyer,  W.  1891.  Ueber  einige  neuere  Forschungen  im  Gebiete 
der  Anatomie  des  Centralnervensystems,  Deutsch.  med.  Woch.,  Bd.  17. 


CHAPTER  IV 

THE   REFLEX   CIRCUITS 

The  cellular  unit  of  the  nervous  system,  as  we  have  seen,  is 
the  neuron.  Neurons,  however,  never  function  independently, 
but  only  when  joined  together  in  chains  whose  connections  are 
correlated  with  the  functions  which  they  serve.  Accordingly, 
the  most  important  unit  of  the  nervous  system,  from  the  phys- 
iological standpoint,  is  not  the  neuron,  but  the  reflex  circuit,  a 
chain  of  neurons  consisting  of  a  receptor  or  seatisory  organ,  a  cor- 
relating center  or  adjuster,  and  an  effector  or  organ  of  response, 
together  with  afferent  and  efferent  nerve-fibers  which  serve  as 
conductors  between  the  center  and  the  receptor  and  effector 
respectively  (see  p.  25).  In  a  reflex  circuit  the  parts  must  be 
so  connected  that  upon  stimulation  of  the  receptive  end-organ  a 
useful  or  adaptive  response  follows,  such,  for  instance,  as  the 
immediate  jerking  away  of  the  hand  upon  accidentally  touching 
a  hot  stove. 

A  reflex  act,  as  this  term  is  usually  defined  by  the  physiologists, 
is  an  invariable  mechanically  determined  adaptive  response  to 
the  stimulation  of  a  sense  organ,  involving  the  use  of  a  center  of 
correlation  and  the  conductors  necessary  to  connect  this  center 
with  the  appropriate  receptor  and  effector  apparatus.  The  act 
is  not  voluntarily  performed,  though  one  may  become  aware  of 
the  reaction  during  or  after  its  performance. 

The  term  "reflex"  is  often  popularly  very  loosely  applied,  but 
as  generally  used  by  physiologists  it  involves  the  rather  complex 
nervous  function  above  described.  If  an  electric  shock  is  ap- 
plied directly  to  a  muscle  or  to  the  motor  nerve  which  innervates 
that  muscle,  the  muscle  will  contract,  but  this  direct  contraction 
is  not  a  reflex  act.  Many  acquired  movements  have  become  so 
habitual  as  to  be  performed  quite  automatically,  such  as  the 
play  of  the  fingers  of  an  expert  pianist  or  typist;  but  these 

56 


THE    REFLEX    CIRCUITS  57 

acquired  automatisms  must  be  clearly  distinguished  from  the 
reflexes,  which  belong  to  the  innate  nervous  organization  with 
which  we  are  endowed  at  birth  (see  pp.  31,  301).  The  lowly 
organisms  which  lack  a  differentiated  nervous  system  exhibit 
many  kinds  of  behavior  which  closely  resemble  reflexes  and,  in 
fact,  are  physiologically  of  the  same  type;  but  these  non-nervous 
responses  are  usually  termed  tropisms  or  taxes,  though  some 
physiologists  call  them  reflexes,  and  some  reflexes,  as  above  de- 
fined, are  often  called  tropisms. 

The  structure  of  the  simple  reflex  circuit  is  diagrammatically 
illustrated  in  Fig.  18,  A.  The  receptor  (R)  may  be  a  simple 
terminal  expansion  of  the  sensory  nerve-fiber  or  a  very  complex 
sense  organ.  The  effector  (E)  may  be  a  muscle  or  a  gland.  The 
cell  body  of  the  afferent  neuron  (1)  may  lie  within  the  center  (C) 
or  outside,  as  in  the  diagram.  The  latter  condition  is  more  usual, 
as  seen  in  the  spinal  and  cranial  ganglia  (Fig.  1,  p.  25).  The 
synapse  and  the  cell  body  of  the  efferent  neuron  (2)  lie  in  the 
center. 

A  simple  reflex  act  involving  the  use  of  so  elementary  a  mech- 
anism as  has  just  been  described  is  probably  never  performed 
by  any  adult  vertebrate.  The  nervous  impulse  somewhere  irl  its 
course  always  comes  into  relation  with  other  reflex  paths,  and  in 
this  way  complications  in  the  response  are  introduced.  Some 
illustrations  of  the  simpler  types  of  such  complex  reflex  circuits 
will  next  be  considered. 

Separate  reflex  circuits  may  be  so  compounded  as  to  give  the 
so-called  chain  reflex  (Fig.  18,  B).  Here  the  response  of  the 
first  reflex  serves  as  the  stimulus  for  the  second,  and  so  on  in 
series.  The  units  of  these  chain  reflexes  are  usually  not  simple 
reflexes  as  diagrammed,  but  complex  elements  of  the  types  next 
to  be  described. 

Figure  18,  C  illustrates  another  method  of  compounding  re- 
flexes so  that  the  stimulation  of  a  single  sense  organ  may  excite 
either  or  both  of  two  responses.  If  the  two  effectors,  El  and 
E2,  can  cooperate  in  the  performance  of  an  adaptive  response, 
the  case  is  similar  to  that  of  Fig.  18,  A,  with  the  possibility  of  a 
more  complex  type  of  reaction.  This  is  an  allied  reflex.  If, 
however,  the  two  effectors  produce  antagonistic  movements,  so 
that  both  cannot  act  at  the  same  time,  the  result  is  a  physiological 


58 


INTRODUCTION   TO    NEUROLOGY 


dilemma.  Either  no  reaction  at  all  results,  or  there  is  a  sort  of 
physiological  resolution  (sometimes  called  physiological  choice), 
one  motor  pathway  being  taken  to  the  exclusion  of  the  other. 
Which  path  will  be  chosen  in  a  given  case  may  be  determined  by 


]) — ^i-^-^-f — ^ 


Fig.  18. — Diagrams  representing  the  relations  of  neurons  in  five  types  of 
reflex  arcs:  A,  Simple  reflex  arc;  B,  chain  reflex;  C,  a  complex  system  illus- 
trating allied  and  antagonistic  reflexes  and  physiological  resolution;  D,  a 
complex  system  illustrating  allied  and  antagonistic  reflexes  with  a  final 
common  path;  E,  a  complex  system  illustrating  the  mechanism  of  physio- 
logical association.  A,  A,  association  neurons;  C,  C,  C",  CI,  and  C3,  centers 
(adjustors);  E,  E',  E",  El,  and  E2,  effectors;  FCP,  final  common  path; 
R,  R',  R",  Rl,  and  R2,  receptors. 

the  physiological  state  of  the  organs.   If,  for  instance,  one  motor 
system,  E2,  is  greatly  fatigued  and  the  other  rested,  the  thresh- 
old of  E2  will  be  raised  and  the  motor  discharge  will  pass  to  El . 
Figure  18,  D  illustrates  the  converse  case,  where  two  receptors 


THE    REFLEX    CIRCUITS  59 

discharge  into  a  single  center,  which,  in  turn,  by  means  of  a  final 
common  path  (FCP)  excites  a  single  effector  (E).  If  the  two  re- 
ceptors upon  stimulation  normally  call  forth  the  same  response, 
they  will  reinforce  each  other  if  simultaneously  stimulated, 
the  response  will  be  strengthened,  and  we  have  another  type  of 
allied  reflex.  But  there  are  cases  in  which  the  stimulation  of 
Rl  and  Rf  (Fig.  18,  D)  would  naturally  call  forth  antagonistic 
reflexes.  Here,  if  they  are  simultaneously  stimulated,  a  phys- 
iological dilemma  will  again  arise  which  can  be  resolved  only  by 
one  or  the  other  afferent  system  getting  control  of  the  final  com- 
mon path. 

Figure  18,  E  illustrates  still  another  form  of  combination  of 
reflexes.  Here  there  are  connecting  tracts  {A,  A)  between  the 
two  centers  so  arranged  that  stimulation  of  either  of  the  two 
receptors  {Rl  and  R2)  may  call  forth  a  response  in  either  one  of 
two  effectors  {El  and  ES).  These  responses  may  be  allied  or 
antagonistic,  and  much  more  complicated  reflexes  are  here  pos- 
sible than  in  any  of  the  preceding  cases. 

A  few  illustrations  of  the  practical  operation  of  these  types 
of  reflex  circuits  will  be  given  here  and  many  other  cases  are 
cited  throughout  the  following  discussions.  A  case  of  a  simple 
reflex  has  already  been  mentioned  in  the  sudden  twitch  of  the 
hand  in  response  to  a  painful  stimulation  of  the  skin.  The 
simplest  possible  mechanism  of  this  reaction  involving  only  two 
neurons  is  shown  in  Fig.  1  (p.  25).  In  actual  practice,  however, 
the  arrangement  figured  is  one  element  only  of  a  more  complex 
reaction  (see  p.  61).  Figure  19  illustrates  a  more  usual  form 
of  this  type  of  reaction,  where  a  series  of  three  or  more  neurons 
is  involved  and  at  least  two  cerebral  centers.  An  auditory  im- 
pulse coming  to  the  brain  from  the  ear  through  the  YIII  cranial 
nerve  terminates  in  a  primary  acoustic  center  in  the  superior 
olive  (a  deep  nucleus  of  the  medulla  oblongata,  see  p.  201), 
where  it  is  taken  up  by  an  intercalary  neuron  of  the  second  order 
and  transmitted  to  the  nucleus  of  the  VI  nerve.  The  result  is  a 
contraction  of  the  external  rectus  muscle  of  the  eyeball;  turning 
the  eye  toward  the  side  from  which  the  auditory  stimulus  was 
received.  So  far  as  this  reaction  alone  is  concerned,  it  is  a  simple 
reflex,  but  in  practice  the  external  rectus  muscle  of  one  e^'e  is 
never  contracted  apart  from  the  other  five  muscles  of  that  eye 


60 


INTRODUCTION  TO   NEUROLOGY 


and  all  six  muscles  of  the  other  eye.  In  this  way  alone  can  con- 
jugate movements  of  the  two  eyes  be  effected  for  the  accurate 
fixation  of  the  gaze  upon  any  object.  The  entire  system  of  con- 
jugate movements  is  also  entirely  reflex  and  it  is  effected  by  an 
exceedingly  complicated  arrangement  of  nerve  tracts  and  cen- 
ters, of  which  the  superior  olive  and  the  nucleus  of  the  VI  nerve 
are  integral  parts. 

The  chain  reflex  (see  Fig.  18,  B)  is  a  very  common  and  a  very 
important  type.  Most  of  the  ordinary  acts  in  the  routine  of 
daily  life  employ  it  in  one  form  or  another,  the  completion  of  one 
stage  of  the  process  serving  as  the  stimulus  for  the  initiation 
of  the  next. 


3ZI  nerve 


Fig.  19. — Diagram  of  a  simple  auditory  reflex.  Upon  stimulation  of  the 
endings  of  the  VIII  nerve  in  the  ear  by  sound  waves,  a  nervous  impulse  may 
pass  to  the  superior  olive,  whence  it  is  carried  by  an  intercalary  neuron  of 
the  second  order  to  the  nucleus  of  the  VI  nerve.  The  fibers  of  this  nerve 
end  on  the  external  rectus  muscle  of  the  eyeball. 


There  are  within  the  muscles  elaborate  sense  organs  (the  mus- 
cle spindles  and  their  associated  afferent  nerves,  see  p.  87), 
which  are  stimulated  by  the  contraction  of  the  muscle.  These 
afferent  nerves  of  the  muscle  sense  have  their  own  centers  of 
adjustment  within  the  central  nervous  system,  from  which  in 
turn  efferent  impulses  go  out  which  ultimately  reach  the  same 
muscles  from  which  the  sensory  impulses  came  in.  This,  of 
course,  is  a  variety  of  chain  reflex,  and  is  the  mechanism  by 
which  refined  movements  of  precision  are  executed,  where  differ- 
ent sets  of  muscles  must  work  against  each  other  in  constantly 
varying  relations  without  conscious  control.  In  the  case  of  a 
sustained  reflex  series  of  this  character  this  return  flow  of  affer- 


THE    REFLEX    CIRCUITS  61 

ent  impulses  of  the  muscle  sense,  tendon  sense,  etc.,  exerts  a 
constant  influence  upon  the  center  which  receives  the  initial 
stimulus,  so  that  this  center  is  constantly  under  the  combined 
influence  of  the  external  stimulus  which  sets  the  reflex  in  motion 
and  the  internal  stimuli  arising  from  the  muscles  themselves 
(proprioceptors,  see  p.  86)  which  control  its  course.  In  this 
case  there  is  a  true  physiological  circuit  rather  than  an  arc  or 
segment  of  a  circuit,  as  is  commonly  implied  in  the  expression 
"reflex  arc."  This  case  is  typical  of  the  complex  reflexes  of  the 
body  in  general,  and  for  this  and  other  considerations  we  follow 
the  usage  of  Dewey  (1893)  and  term  the  mechanism  of  a  com- 
plete reflex  a  "reflex  circuit"  rather  than  an  arc  (see  C.  J. 
Herrick,  1913,  and  p.  308). 

It  has  been  suggested  by  Loeb  also  that  many  instincts  are 
simply  complex  chain  reflexes.  Even  in  animals  whose  behavior 
is  so  complex  as  birds,  a  careful  analysis  of  the  cycle  of  nest 
building  and  rearing  of  young  reveals  many  clear  illustrations  of 
this  principle  (see  the  works  of  F.  H.  Herrick,  cited  at  the  end  of 
this  chapter).  Each  step  in  the  cycle  is  a  necessary  antecedent 
to  the  next,  and  if  the  series  is  interrupted  it  is  often  necessary 
for  the  birds  to  go  back  to  the  beginning  of  the  cycle.  They 
cannot  make  an  intelligent  adjustment  midway  of  the  series. 

The  complex  circuit  illustrated  by  Fig.  18,  C  presents  two 
possible  types  of  reaction,  either  allied  or  antagonistic  reflexes. 
The  former  case  is  illustrated  again  by  the  sudden  movement  of 
the  hand  in  response  to  a  painful  stimulation  of  the  skin.  This 
is  brought  about,  as  we  saw  in  considering  the  simple  reflex,  by  a 
contraction  of  the  arm  muscles.  But  the  muscles  which  move 
the  elbow-joint  are  not,  when  the  arm  is  at  rest,  entirely  flaccid. 
Both  flexors  and  extensors  are  always  contracted  to  a  certain 
degree,  one  balanced  against  the  other.  Now  at  the  same  time 
that  the  sensory  stimulus  from  R  (see  Fig.  18,  C)  causes  the  con- 
traction of  the  flexor  muscle,  El ,  it  also  causes  the  relaxation  of 
the  antagonistic  extensor,  E2  the  two  efferent  impulses  coopera- 
ting to  effect  the  avoiding  reaction  as  rapidly  as  possible.  In 
the  antagonistic  reflexes  of  our  third  type  the  physiological  reso- 
lution involved  in  the  selection  of  one  or  the  other  possible 
reaction  always  involves  a  delay  in  the  response  until  one  motor 
pathway  dominates  the  system  to  the  exclusion  of  the  other. 


62 


INTRODUCTION   TO   NEUROLOGY 


In  the  fourth  type  of  complex  reflexes  (see  Fig.  18,  D)  two  dif- 
ferent sensory  paths  discharge  into  a  single  center,  from  which  a 
final  common  path  goes  out  to  the  effector.  This  mechanism 
also  provides  for  both  allied  and  antagonistic  reflexes.  A  very 
simple  apparatus  for  this  type  of  reflex  is  found  in  the  roof  of  the 
midbrain  of  the  lowly  amphibian,  the  common  mud  puppy, 
Necturus.  Here  the  upper  part  of  the  midbrain  roof  receives 
optic  fibers  from  the  optic  tracts,  while  the  lower  part  receives 
fibers  from  the  primary  acoustic  and  tactile  centers  (Fig.  20). 


OPTIC 

CENTER 


m  nerve 


MOTOR 
CENTER 


Fig.  20. — Diagram  of  a  cross-section  through  the  midbrain  of  Necturus, 
illustrating  a  single  correlation  neuron  of  the  midbrain  roof.  One  dendrite 
spreads  out  in  the  optic  center  among  terminals  of  the  optic  tracts;  another 
dendrite  similarly  spreads  out  in  the  acoustic  and  tactile  center.  The  axon 
descends  to  connect  with  the  motor  neurons  of  the  III  nerve. 


A  single  neuron  of  the  midbrain  may  send  one  dendrite  down- 
ward to  receive  acoustic  or  tactile  stimuli  (or  both  of  these),  and 
another  dendrite  upward  to  receive  optic  stimuli.  If  the  animal 
receives  visual  and  auditory  stimuli  simultaneously,  the  inter- 
calary neuron  of  the  midbrain  may  be  excited  by  both  sets  of 
stimuli.  Its  discharge  through  the  axon  to  the  motor  organs  of 
response  (say  to  the  eye  muscles  by  way  of  the  III  nerve,  as  in 
Fig.  20)  will  be  the  physiological  resultant  of  both  sets  of  ex- 
citations.    If  they  reinforce  each  other,  the  discharge  will  be 


THE    REFLEX    CIRCUITS 


63 


stronger  and  more  rapid;  if,  on  the  other  hand,  they  tend  to  pro- 
duce antagonistic  responses,  there  will  be  an  inhibition  of  the 
response  or  a  dela}^  until  one  or  the  other  stimulus  obtains  the 
mastery. 

Yerkes  has  given  a  striking  illustration  of  this  method  of  re- 
inforcement of  stimuli  in  his  experiments  on  the  sense  of  hearing 
in  frogs.  The  reflex  mechanism  of  touch,  hearing,  and  vision  in 
the  midbrain  of  the  frog  is  similar  to  that  of  Xecturus  as  des- 
cribed above  (Fig.  20).     Yerkes  found  that  frogs  under  labora- 


midbram 


5£:!^:^emisphere 


erve 


Fig.  21. — Diagram  of  some  conduction  paths  in  the  brain  of  Nectm"us, 
seen  in  longitudinal  section.  From  the  medulla  oblongata  an  acoustic 
impulse  may  be  carried  forward  through  the  nem-on  A  to  the  midbrain, 
whose  nem'ons,  B,  are  of  the  type  shown  in  Fig.  20,  receiving  both  acoustic 
and  optic  impulses.  This  neuron,  B,  may  discharge  do^\mward  through  the 
tract  S  to  the  motor  nuclei  of  the  III,  V,  VII,  etc.,  nerves,  or  it  may  dis- 
charge upward  to  a  neuron  of  the  thalamus,  f,  which  also  receives  descend- 
ing impulses  from  the  cerebral  hemisphere  through  the  neuron,  D,  and,  in 
turn,  discharges  through  the  motor  tract,  S. 


tory  conditions  do  not  ordinarily  react  at  all  to  sounds  alone, 
but  that  they  do  react  to  tactual  and  visual  stimuli.  When 
these  reactions  are  carefully  measured,  it  is  found  that  the  sound 
of  an  electric  bell  occurring  simultaneously  with  a  tactual  or 
visual  stimulus  markedly  increases  (reinforces)  the  strength  of 
the  reaction. 

The  reflex  centers  of  the  midbrain  are  further  complicated  bj' 
the  fact  that  the  efferent  tract  from  the  sensory  centers  above 
the  aqueduct  of  Sylvius  is  not  simple  as  diagrammed  in  Fig. 
20,  but  it  divides  into  a  descending  and  an  ascending  path,  as 


64  INTRODUCTION   TO    NEUROLOGY 

shown  by  the  neuron  B  of  Fig.  21.  The  descending  path 
connects  directly  with  motor  centers,  including  the  oculomotor, 
bulbar,  and  spinal  motor  nuclei  (Fig.  21,  S),  while  the  ascending 
path  enters  the  thalamus,  where  associations  of  a  still  higher 
order  are  effected  through  the  thalamic  neuron,  C.  Here  again  is 
introduced  a  physiological  choice  or  dilemma;  the  response  is  not 
a  simple  mechanical  resultant  of  the  interacting  stimuli,  but  its 
character  may  be  influenced  by  variable  physiological  states. 
The  invariable  type  of  action  is  replaced  by  a  relatively  variable 
or  labile  type  (see  p.  31).  In  the  thalamus  the  nervous  impulse 
is  again  subjected  to  modification  under  the  influence  of  a  still 
greater  variety  of  afferent  impulses,  for  these  centers  receive  all 
sensory  types  found  in  the  midbrain,  and,  in  addition,  important 
descending  tracts  from  the  cerebral  hemispheres  (in  lower  ver- 
tebrates the  latter  are  chiefly  olfactory). 

The  more  complicated  associations  are  effected  by  arrange- 
ments of  correlation  tracts  and  centers  illustrated  in  the  simplest 
possible  form  by  Fig.  18,  E.  The  mode  of  operation  of  such 
a  system  may  be  illustrated  by  an  example :  A  collie  dog  which  I 
once  owned  acquired  the  habit  of  rounding  up  my  neighbor's 
sheep  at  very  unseasonable  times.  The  sight  of  the  flock  in  the 
pasture  (stimulus  Rl,  Fig.  18,  E)  led  to  the  pleasurable  reaction 
(El)  of  chasing  the  sheep  up  to  the  barnyard.  It  became  neces- 
sary to  break  up  the  habit  at  once  or  lose  a  valuable  dog  at  the 
hands  of  an  angry  farmer  with  a  shotgun.  Accordingly,  I 
walked  out  to  the  pasture  with  the  dog.  She  at  once  brought  in 
the  sheep  of  her  own  accord  and  then  ran  up  to  me  with  every 
expression  of  canine  pride  and  self-satisfaction,  whereupon  I 
immediately  gave  her  a  severe  whipping  (stimulus  R2).  This 
called  forth  the  reaction  {E2)  of  running  home  and  hiding  in  her 
kennel.  The  next  day  (the  dog  and  I  having  meanwhile  with 
mutual  forgiveness  again  arrived  at  friendly  relations)  we  took  a 
walk  in  a  different  direction,  in  the  course  of  which  we  unex- 
pectedly met  another  flock  of  sheep.  At  sight  of  these  the  dog 
immediately,  with  no  word  from  me,  put  her  tail  between  her 
legs,  ran  home  as  fast  as  possible,  and  hid  in  her  kennel.  Here 
the  stimulus  Rl  led  not  to  its  own  accustomed  response,  El, 
but  to  ES,  evidently  under  the  influence  of  vestigeal  traces  of  the 
previous  day's  experience,  wherein  the  activities  of  CI  and  C2 


THE    REFLEX    CIRCUITS  65 

were  related  through  the  associational  tract  (A,  A)  passing  be- 
tween them. 

In  the  case  of  the  dog's  experience  just  described  the  neural 
mechanism  was  undoubtedly  much  more  complex  than  our  dia- 
gram, though  similar  in  principle,  and  the  associative  memory 
process  involved  was  probably  vividly  conscious  (cf.  p.  295). 
But  the  simpler  types  of  "associative  memory"  which  have  been 
experimentally  demonstrated  in  many  of  the  lower  organisms 
may  involve  no  more  complex  mechanism  than  this  diagram,  and 
it  is  by  no  means  certain  that  any  conscious  process  is  there 
present. 

It  must  be  kept  in  mind  that  in  higher  vertebrates  all  parts  of 
the  nervous  system  are  bound  together  by  connecting  tracts 
(internuncial  pathways).  Some  of  these  tracts  are  long,  well- 
defined  bundles  of  myehnated  fibers  whose  connections  are  such 
as  to  facilitate  uniform  and  clear-cut  responses  to  stimulation. 
Others  are  very  diffuse  and  poorly  integrated.  Permeating  the 
entire  central  nervous  system  is  an  entanglement  of  very  deli- 
cate short  unmyehnated  fibers.  This  nervous  felt-work  (neuro- 
pil) is  much  more  highly  developed  in  some  parts  of  the  brain 
than  in  others.  It  is  not  well  adapted  to  conduct  definite  ner- 
vous impulses  for  long  distances,  but  it  may  serve  to  diffuse  or 
irradiate  such  impulses  widely.  Where  tissue  of  this  sort  is 
mingled  with  myelinated  fibers  it  is  termed  the  "reticular  for- 
mation" (see  pp.  65,  127,  158,  304). 

These  manifold  connections  are  so  elaborate  that  every  part 
of  the  nervous  system  is  in  nervous  connection  with  every  other 
part,  directly  or  indirectly.  This  is  illustrated  by  the  way  in 
which  the  digestive  functions  (which  normally  are  quite  auton- 
omous, the  nervous  control  not  going  beyond  the  sympathetic 
system,  see  p.  241)  may  be  disturbed  by  mental  processes  whose 
primary  seat  may  be  in  the  association  centers  of  the  cerebral 
cortex;  and  also  by  the  way  in  which  strychnin-poisoning 
seems  to  lower  the  neural  resistance  everywhere,  so  that  a 
very  slight  stimulus  may  serve  to  throw  the  whole  body  into 
convulsions. 

It  follows  that  the  locahzation  of  cerebral  functions  can  be 
only  approximate.  Every  normal  activity  has  what  Sherring- 
ton calls  its  reflex  pattern,  whose  anatomical  basis  is  a  definite 
5 


66  INTRODUCTION  TO  NEUROLOGY 

reflex  path;  but  the  stimulus  is  rarely  simple  and  the  nervous 
discharge  irradiates  more  or  less  widely,  so  that  the  activity  is 
by  no  means  limited  to  the  part  which  gives  the  act  its  reflex 
pattern.  Moreover,  neither  the  stimulus  complex  nor  the  char- 
acter of  the  irradiation  will  be  repeated  exactly  in  any  higher 
animal,  so  that  the  precise  nature  of  the  response  cannot  in  any 
case  be  infallibly  predicted  except  under  experimental  conditions 
(and  not  always  then). 

Our  picture  of  the  reflex  act  in  a  higher  animal  will,  then, 
include  a  view  of  the  whole  nervous  system  in  a  state  of  neural 
tension.  The  stimulus  disturbs  the  equilibrium  at  a  definite 
point  (the  receptor),  and  the  wave  of  nervous  discharge  thus  set 
up  irradiates  through  the  complex  lines  determined  by  the  neural 
connections  of  the  receptor.  If  the  stimulus  is  weak  and  the 
reflex  path  is  simple  and  well  insulated,  a  simple  response  may 
follow  immediately.  Under  other  conditions  the  nervous  dis- 
charge may  be  inhibited  before  it  reaches  any  effector,  or  it  may 
irradiate  widely,  producing  a  very  complex  reflex  pattern.  In 
the  former  case  the  neural  equilibrium  will  be  only  locally 
disturbed;  in  the  latter  case  almost  the  whole  nervous  system 
may  participate  in  the  reaction,  a  part  focal  and  sharply  defined 
and  the  rest  marginal,  diffuse,  and  exercising  more  or  less  of 
inhibitory  or  reinforcing  control  on  the  final  reaction. 

The  studies  of  Herrick  and  Coghifl  have  shown  that  in  the 
development  of  the  nervous  system  of  Amphibia  the  first  reflex 
circuits  to  come  to  maturity  are  made  up  of  rather  complex 
chains  of  neurons  so  arranged  as  to  permit  of  only  one  type  of 
response,  viz.,  a  total  reaction  (the  swimming  movement),  from 
all  possible  forms  of  stimulation,  and  that  in  successive  later 
stages  this  generalized  type  is  gradually  replaced  by  a  series  of 
special  reflexes  involving  more  diversified  movements.  Parallel 
with  this  process  the  higher  correlation  centers  are  developed 
for  the  integration  of  the  several  special  reflexes  into  complex 
action  systems.  The  simple  reflex  arc,  as  illustrated  in  Fig. 
1  (p.  25),  which  is  adapted  for  the  execution  of  a  single  movement 
in  response  to  a  particular  stimulus,  is  the  final  stage  in  this 
developmental  process,  whose  initial  stages  are  much  more 
complex  and  diffuse  arrangements  of  neurons  adapted  for  total 
reactions  of  a  more  general  sort. 


THE    REFLEX    CIRCUITS  67 

We  have  just  described  the  mechanisms  of  certain  reflexes. 
The  question  at  once  arises,  In  what  sense  do  we  know  the 
mechanism  of  a  nervous  reaction?  Certainly  not  in  the  sense 
that  we  understand  all  of  the  factors  involved  in  nervous  conduc- 
tion and  correlation.  But  we  do  have  a  practical  knowledge  of 
the  combinations  of  neurons  necessary  to  effect  certain  definite 
results,  much  as  the  practical  electrician  may  be  able  to  wind  a 
dynamo  or  build  a  telephone,  even  though  his  knowledge  of  the 
theory  of  electricity  be  very  small. 

Summary. — The  reflex  arcs  or  reflex  circuits  rather  than 
the  neurons  of  which  these  circuits  are  composed  are,  from 
the  physiological  standpoint,  the  most  important  units  of  the 
nervous  system.  Reflex  acts  are  to  be  distinguished,  on  the 
one  hand,  from  the  simpler  non-nervous  reactions  known  as 
tropisms  and  taxes,  and,  on  the  other  hand,  from  voluntary 
acts  and  acquired  automatisms.  Many  instincts  are  chain 
reflexes  of  very  complex  sorts,  the  completion  of  one  reaction 
serving  as  the  stimulus  for  the  next,  and  so  on  in  series.  The 
simplest  true  reflex  requires  a  receptor,  a  center  or  adjustor, 
an  effector,  and  the  afferent  and  efferent  conductors  which  put 
the  center  into  physiological  relation  with  the  receptor  and  the 
effector  respectively.  Five  types  of  reflex  circuits  were  distin- 
guished (see  Fig.  18)  and  illustrations  of  them  given.  All  of  the 
reflex  centers  are  interconnected  by  systems  of  fibers,  either  in 
the  form  of  definite  tracts  or  else  by  more  diffuse  connections 
in  the  neuropil.  Localization  of  cerebral  function  is,  therefore, 
only  approximate,  with  the  possibility  of  all  sorts  of  intercon- 
nection of  different  reflex  systems  as  occasion  may  require. 
This  is  the  neurological  basis  of  the  greater  plasticity  of 
behavior  of  higher  vertebratesas  contrasted  with  invertebrates 
and  lower  vertebrates. 

Literature 

Dewey,  J.  1893.  The  Reflex  Arc  Concept  in  Psychology,  Psychol. 
Review,  vol.  iii,  p.  357. 

Herrick,  C.  Judson.  1913.  Some  Reflections  on  the  Origin  and  Sig- 
nificance of  the  Cerebral  Cortex,  Jour,  of  Animal  Behavior,  vol.  iii,  pp.  222- 
236. 

Herrick,  C.  Judson  and  Coghill,  G.  E.  1915.  The  Development  of 
Reflex  Mechanisms  in  Amblystoma,  Jour.  Comp.  Neur.,  vol.  xxv,  pp.  65-85. 


68  INTRODUCTION  TO  NEUROLOGY 

Herrick,  F.  H.  1905.  The  Home  Life  of  Wild  Birds.     Revised  edition, 
New  York. 

— .  1907.  Analysis  of  the  Cyclical  Instincts  of  Birds,  Science,  N.  S.,  vol. 
XXV,  pp.  725,  726;  and  Jour.  Comp.  Neur.,  vol.  xvii,  pp.  194,  195. 

— .  1907.  The  Blending  and  Overlap  of  Instincts,  Science,  N.  S.,  vol. 
XXV,  pp.  781,  782;  and  Jour.  Comp.  Neur.,  vol.  xvii,  pp.  195-197. 

— .  1908.  The  Relation  of  Instinct  to  Intelligence  in  Birds,  Science, 
N.  S.,  vol.  xxvii,  pp.  847-850. 

Hough,  Th.  1915.  The  Classification  of  Nervous  Reactions,  Science, 
N.  S.,  vol.  xli,  pp.  407^18. 

Jennings,  H.  S.  1905.  The  Basis  for  Taxis  and  Certain  Other  Terms  in 
the  Behavior  of  Infusoria,  Jour.  Comp.  Neur.,  vol.  xv,  pp.  138-143. 

— .  1906.  The  Behavior  of  Lower  Organisms,  New  York. 

LoEB,  J.  1900.  Comparative  Physiology  of  the  Brain  and  Comparative 
Psychology,  New  York. 

— .  1912.  The  Mechanistic  Conception  of  Life,  Chicago. 

Sherrington,  C.  S.  1906.  The  Integrative  Action  of  the  Nervous  Sys- 
tem, New  York. 

Yerkes,  R.  M.  1905.  The  Sense  of  Hearing  in  Frogs,  Jour.  Comp.  Neur., 
vol.  XV,  pp.  279-304. 


CHAPTER  V 
THE    RECEPTORS   AND    EFFECTORS 

In  the  further  study  of  the  nervous  system  as  the  apparatus 
of  adjustment  between  the  activities  of  the  body  and  those  of 
environing  nature,  our  first  task  is  the  analysis  of  the  receptors 
(that  is,  the  sense  organs) ;  for  these  are  the  only  places  through 
which  the  forces  of  the  world  outside  can  reach  the  nervous  sys- 
tem in  order  to  excite  its  activity. 

"The  world  is  so  full  of  a  number  of  things 
I'm  sure  we  should  aU  be  as  happy  as  kings." 

But  in  order  to  attain  this  fortunate  result  it  is  necessary  that  we 
should  be  able  to  discriminate  the  essential  from  the  unimportant 
elements  of  this  environing  complex,  and  to  adjust  our  own  be- 
havior in  relation  thereto. 

Protoplasm  in  its  simplest  form  is  sensitive  to  some  sorts  of 
mechanical  and  chemical  stimulation.  In  fact,  as  we  have  seen, 
all  of  the  so-called  nervous  functions  are  implicit  in  undifferen- 
tiated protoplasm.  But  the  bodies  of  all  but  a  few  of  the  lowest 
organisms  are  protected  by  some  sort  of  a  shell  or  cuticle  from 
excessive  stimulation  from  the  outside,  and  individual  parts  of 
the  surface  are  then  differentiated  in  such  a  way  as  to  be  sensi- 
tive to  only  one  group  of  excitations  while  remaining  insensitive 
to  all  other  forms.  Thus  arose  the  sense  organs,  each  of  which 
consists  essentially  of  specialized  protoplasm  which  is  highly 
sensitive  to  some  particular  form  of  energy  manifestation,  but 
relatively  insensitive  to  other  forms  of  stimulation.  Each  sense 
organ  possesses,  in  addition,  certain  accessory  parts,  adapted  to 
concentrate  the  stimuli  upon  the  essential  sensitive  protoplasm, 
to  intensify  the  force  of  the  stimulus,  or  to  so  transform  the 

69 


70  INTRODUCTION   TO    NEUROLOGY 

energy  of  the  stimulus  as  to  enable  it  to  act  more  efficiently  upon 
the  essential  end-organ. 

Sherrington  states  the  distinctive  characteristic  of  the  sense 
organs  in  this  form,  "The  main  function  of  the  receptor  is,  there- 
fore, to  lower  the  threshold  of  excitability  of  the  arc  for  one  kind 
of  stimulus  and  to  heighten  it  for  all  others."  The  selective  func- 
tion of  the  receptors  is  illustrated  by  a  consideration  of  the 
different  forms  of  vibratory  energy  which  pervade  the  environ- 
ment in  which  we  live. 

There  are,  first,  rhythmically  repeated  mechanical  impacts 
perceived  through  the  sense  of  touch.  This  series  of  tactile 
sensations  extends  from  a  single  isolated  contact  at  one  extreme 
to  rhythmically  repeated  contacts  touching  the  skin  as  fre- 
quently as  1552  vibrations  per  second. 

A  second  series  of  vibratory  phenomena  is  presented  by  the 
mechanical  vibrations  of  the  surrounding  medium  perceived  sub- 
jectively as  sound.  Out  of  the  entire  series  of  such  vibrations  of 
all  possible  frequencies  the  human  ear  is  sensitive  to  a  series  of 
approximately  ten  octaves  from  about  30  (in  some  cases  12)  to 
about  30,000  (in  some  cases  50,000)  vibrations  per  second  (wave 
lengths  from  1228  cm.  or  40  ft.  to  1.3  cm.  or  .5  inch  in  length). 
To  all  other  vibrations  it  is  insensitive.  Within  this  range  the 
average  human  ear  can  discriminate  some  11,000  different  pitch 
qualities  (Titchener). 

Subjectively,  the  series  of  tone  sensations  is  broken  up  into 
a  number  of  octaves,  and  it  is  found  that  a  given  tone  of  th^ 
musical  scale  is  excited  by  vibrations  of  exactly  twice  the  fre- 
quency which  excites  the  corresponding  tone  of  the  next  lower 
octave.  By  analogy  with  this  arrangement  all  series  of  physical 
vibrations  are  sometimes  spoken  of  as  divisible  into  octaves, 
the  octave  being  defined  as  those  vibration  frequencies  which 
lie  between  a  given  rate  and  twice  that  rate  or  half  that 
rate. 

A  third  type  of  vibratory  phenomena  is  presented  by  the  much 
more  rapid  series  of  so-called  ethereal  vibrations,  or  waves  in 
immaterial  media.  The  lower  members  of  this  series  are  the 
Hertzian  electric  waves;  the  higher  members  are  the  a;-rays. 
Between  these  extremes  lie  waves  perceived  as  radiant  heat,  the 
light  waves,  and  the  ultra-violet  rays  of  the  spectrum.     This 


THE  RECEPTORS  AND  EFFECTORS  71 

series  of  ethereal  vibrations  may  extend  farther  indefinitely  both 
downward  and  upward,  but  of  its  ultimate  limits  we  have  no 
knowledge. 

There  is  no  human  sense  organ  which  can  respond  directly  to 
the  electric  waves,  the  ultra-violet  rays,  and  the  a:-rays. 
These  have,  accordingly,  remained  wholly  unknown  to  us  until 
revealed  indirectly  by  the  researches  of  the  physical  laboratories. 
Some  ten  octaves  of  this  series  are  contained  in  the  solar  spec- 
trum, from  an  infra-red  wave  length  of  about  .1  mm.  to  an  ultra- 
violet wave  length  of  .00035  mm.  The  light  from  metallic  arcs 
and  from  incandescent  gases  has,  however,  been  found  to  contain 
wave  lengths  as  short  as  .00006  mm.  The  human  eye  is  sensi- 
tive to  something  over  one  octave  of  this  series  (waves  from 
.0008  to  .0004  mm.  in  length,  whose  rates  lie  between  400,000 
and  800,000  billions  of  vibrations  per  second),  with  six  octaves 
in  the  infra-red  and  three  in  the  ultra-violet.  The  lower  mem- 
bers of  this  series  of  vibrations  of  the  solar  spectrum,  and  to  a 
less  extent  the  higher  also,  are  capable  of  stimulating  the  tem- 
perature organs  of  the  skin. 

Thus  it  appears  that  of  the  complete  series  of  ethereal  vibra- 
tions, we  can  sense  directly  only  about  one  octave  by  the  eye  and 
a  number  of  others  through  the  sense  organs  for  temperature  in 
the  skin,  while  to  the  lowest  and  highest  members  of  the  series 
our  sense  organs  are  entirely  insensitive.  The  sensitivity  of  the 
skin  to  these  vibrations  is  limited  subjectively  to  a  small  range 
of  temperature  sensations,  while  the  retinal  excitations  give  us 
subjectively  an  extensive  series  of  sensations  of  color  and  bright- 
ness. The  human  eye  can  discriminate  from  150  to  230  pure 
spectral  tints,  besides  various  degrees  of  intensity  and  purity  of 
tone,  making  a  total  of  between  500,000  and  600,000  possible 
discriminations  by  the  visual  organs  (von  Kries).  Some  of  the 
preceding  data  are  summarized  in  the  table^  on  page  73. 

^  In  the  preparation  of  this  table  I  have  been  assisted  by  Professor  R.  A. 
MilUkan,  of  the  University  of  Chicago,  whose  kindness  I  gratefully  ac- 
knowledge.    The  figures  given  are  based  upon  the  formula — 

velocity 

i — ^-r  =  rate 

wave  length 

and  the  velocity  of  transmission  is  taken  as  3  x  lO^"  cm.  per  second.     The 

actual  velocity  of  light  waves  as  worked  out  experimentally  by  Michelson 

is  299,853  kilometers  per  second. 


72 


INTRODUCTION   TO   NEUROLOGY 
TABLE  OF  PHYSICAL  VIBRATIONS 


Physical 
process. 

Wave 
length. 

Number  of  vibrations 
per  second. 

Receptor. 

Sensation. 

Mechanical 

From  very  slow 

to 
1552  per  second. 

Skin. 

Touch  and 

contact. 

Below  12,280  mm. 

Below  30  per  second. 

None. 

None. 

Waves  in 
material 
media. 

12,280  mm. 

to 

13  mm. 

30  per  second 

to 

30,000  per  second. 

Internal 
ear. 

Tone. 

Above  13  mm. 

Above  30,000  per  second. 

None. 

None. 

00  to  .1  mm. 
(electric  waves). 

0  to  3000  billion  (3X10i2). 

None. 

None. 

.1  mm. 

to 
.0004  mm. 

3000  billion  (3X10^2) 

to 

800,000  billion  (8X10W). 

Skin. 

Radiant 
heat. 

Ether  waves. 

.0008  mm. 

to 
.0004  mm. 

400,000  billion  (4  X  10") 

to 
800,000  billion  (8X10"). 

Retina. 

Light  and 
color. 

.0004  mm. 

to 

.000059  mm. 

(ultra-violet-rays) . 

800,000  billion  (8  X  10") 

to 

5,100,000  billion  (5.1  XlO'^). 

None. 

None. 

.0000008  mm. 

to 
.00000005  mm. 

(x-rays). 

400,000,000  billion  (4  X  lO^') 

to 
6,000,000,000  billion  (GXlO'S). 

None. 

None. 

Similarly,  the  chemical  senses,  taste  and  smell,  reveal  to  us  only 
a  very  small  number  out  of  the  total  series  of  actual  excitations 
to  which  our  sense  organs  are  exposed.  Our  organs  of  taste,  in 
fact,  can  respond  to  only  four  types  of  chemical  substances,  with 
only  four  subjective  sense  quahties,  viz.,  sour,  salty,  sweet,  bitter. 
The  organs  of  smell  respond  to  a  larger  range  of  chemical  stimuli 
and  to  far  greater  dilutions,  i.  e.,  the  threshold  of  sensation  is 
far  lower  for  smell  than  for  taste. 

Many  of  the  lower  animals  have  very  different  limits  of  sus- 
ceptibility to  the  kinds  of  stimulation  which  we  have  just  been 
considering,  and  in  some  cases  they  have  sense  organs  which  are 
attuned  to  respond  to  a  quite  different  series  of  environmental 
factors  than  are  our  own,  as,  for  example,  the  lateral  line  sense 
organs  of  fishes.  We  can  form  no  idea  how  the  world  appears  to 
such  organisms  except  in  so  far  as  their  sensory  equipment  is 
analogous  with  our  own. 


THE  RECEPTORS  AND  EFFECTORS  73 

From  these  illustrations  it  is  plain  that  the  sensory  equipment 
of  the  human  body  is  adapted  to  respond  directly  to  only  a 
limited  part  of  the  environing  energy  complex,  the  remainder 
having  little,  if  any,  practical  significance  in  the  natural  environ- 
ment of  primitive  man.  During  the  progress  of  the  develop- 
ment of  human  culture  mankind  has  very  considerably  wid- 
ened his  contact  with  the  environment  by  artificial  aids  to  his 
sense  organs.  The  range  of  vision  has  been  extended  by  the 
microscope  and  the  telescope,  and  of  hearing  by  the  micro- 
phone and  the  telephone.  The  photographic  plate  enables  him 
to  extend  his  knowledge  of  the  solar  spectrum  beyond  its  visible 
limits,  and  the  Marconi  wireless  apparatus  brings  the  Hertzian 
electric  waves  under  his  control  and  thus  enables  him  to 
put  a  girdle  round  about  the  earth  in  less  than  Puck's  forty 
minutes. 

We  may  conceive  the  body  as  immersed  in  a  world  full  of 
energy  manifestations  of  diverse  sorts,  but  more  or  less  com- 
pletely insulated  from  the  play  of  these  cosmic  forces  by  an 
impervious  cuticle.  The  bodily  surface,  however,  is  permeable 
in  some  places  to  these  environing  forces  and  in  a  differential 
fashion,  one  part  responding  to  a  particular  series  of  vibrations, 
another  part  to  a  different  series,  much  as  the  strings  of  a  piano 
when  the  dampers  are  lifted  will  vibrate  sympathetically  each  to 
its  own  tone  when  a  musical  production  is  played  on  a  neighbor- 
ing instrument.  The  sense  organs,  again,  may  be  compared 
with  windows,  each  of  which  opens  out  into  a  particular  field  so 
as  to  admit  its  own  special  series  of  environmental  forces.  In 
each  species  of  animals  these  windows  are  arranged  in  a  charac- 
teristic way,  so  as  to  admit  only  those  forms  of  energy  which  are 
of  practical  significance  to  that  animal  as  it  lives  in  its  own  natu- 
ral environment.  The  sensory  equipment  of  the  human  race  was 
thus  established  by  the  biological  necessities  of  our  immediate 
animal  ancestors,  and  there  is  no  evidence  of  subsequent  im- 
provement in  these  physiological  mechanisms  or  of  anj'  increase 
in  the  number  of  our  senses  during  the  advancement  of  human 
culture.  What  the  progress  of  science  has  accomplished  is  to 
supplement  the  limited  sensory  equipment  of  primitive  man  by 
various  indirect  means.  To  recur  to  our  analogy  of  a  house  with 
many  windows,  we  have  not  been  able  to  increase  the  number  of 


74  INTEODUCTION  TO  NEUROLOGY 

windows  so  as  to  look  out  directly  into  new  fields;  but  we  have 
increased  the  range  of  vision  through  the  old  windows,  much  as  a 
telescope  brings  remote  objects  near  and  as  a  periscope  enables 
the  observer  to  see  around  a  corner.  To  the  development  of 
the  cerebral  cortex  we  owe  the  acquisition  of  these  new  powers 
which  have  opened  to  us  the  realms  of  electric  vibrations, 
ultra-violet  rays,  and  many  other  natural  phenomena  to  which 
our  unaided  sense  organs  are  quite  insensitive. 

Children  in  the  kindergarten  are  taught  that  there  are  five 
senses.  In  reality,  there  are  more  than  twenty  different  senses. 
Some  of  the  sense  organs  are  stimulated  by  external  objects  and 
hence  are  termed  exteroceptors ;  others  are  stimulated  by  internal 
excitations  of  the  visceral  organs  and  are  termed  interoceptors. 
Still  further  classifications  have  been  suggested,  to  which  refer- 
ence will  be  made  shortly.  Here  we  must  first  consider  the 
criteria  in  accordance  with  which  the  various  senses  are  dis- 
tinguished. 

The  analysis  and  classification  of  the  senses  is  by  no  means 
so  simple  a  task  as  one  might  at  first  suppose.  It  is  true  that 
ordinarily  we  do  not  confuse  a  thing  seen  with  a  sound  heard; 
but,  on  the  other  hand,  we  do  constantly  confuse  savors  with 
odors,  and  it  often  requires  refined  physiological  experimentation 
to  determine  whether  the  organ  of  taste  or  the  organ  of  smell  is 
the  source  of  the  sensory  excitation  in  question.  Most  of  the 
common  "flavors"  of  food  are,  in  reality,  odors  and  are  perceived 
by  the  organ  of  smell  only.  A  bad  cold  which  closes  the  pos- 
terior nasal  passages  makes  "all  food  taste  alike"  for  this  reason. 
In  reality,  as  we  have  already  seen,  there  are  only  four  tastes 
recognized  by  the  physiologists,  viz.,  sweet,  sour,  salty,  and 
bitter. 

Confusion  has  arisen  in  the  attempts  to  analyze  these  two 
senses  from  the  fact  that  different  physiologists  have  used  differ- 
ent definitions  of  a  "sense."  One  author,  who  defines  these 
senses  in  terms  of  the  physical  agents  which  excite  them,  says 
that  taste  is  stimulated  by  liquids  and  smell  by  vapors,  and  that, 
accordingly,  aquatic  animals,  whose  nostrils  are  filled  with  water, 
have  by  definition  no  sense  of  smell.  Other  authors  separate 
these  senses  according  to  the  organ  stimulated,  the  excitation  of 
the  nose  being  smell,  that  of  the  taste-buds  being  taste,  regard- 


THE  RECEPTORS  AND  EFFECTORS  75 

less  of  the  nature  of  the  exciting  substance  or  of  the  subjective 
quality  of  the  sensation. 

There  are,  in  reality,  four  different  factors  which  must  be 
taken  into  account  in  defining  a  ''sense."  (1)  Doubtless  with  us 
human  folk  the  most  important  criterion  is  direct  introspective 
experience,  the  psychological  criterion.  Ordinarily  this  is  ade- 
quate, but,  as  we  have  just  seen,  there  are  some  cases  where 
it  alone  cannot  be  depended  upon  to  distinguish  between  two 
senses.  (2)  The  adequate  stimuli  of  the  various  senses  exhibit 
characteristic  physical  or  chemical  differences,  the  -physical 
criterion.  This  factor,  too,  must  be  carefully  investigated  or  we 
may  be  led  astray.  (3)  The  data  of  anatomy  and  experimental 
phj^siology  may  differentiate  structurally  the  receptive  organs 
and  conduction  paths  of  the  several  types  of  sensation,  the  ana- 
tomical criterion.  (4)  Finally,  the  type  of  response  varies  in  a 
characteristic  way  for  the  different  senses,  the  physiological 
criterion. 

The  fourth  criterion  has  been  appHed  to  solve  the  problem  of 
the  reason  for  the  development  of  two  very  different  types  of 
sense  organs  and  cerebral  connections  for  the  senses  of  smell  and 
taste,  both  of  which  are  chemical  senses  with  similar  subjective 
qualities.  It  has  been  pointed  out  by  Sherrington  that  taste  is 
an  interoceptive  sense,  calling  forth  visceral  responses  within  the 
body,  while  smell  is,  in  part  at  least,  an  exteroceptive  sense,  being 
excited  by  objects  at  a  distance  from  the  body  and  calling  forth 
movements  of  locomotion  carrying  the  whole  body  toward  or 
away  from  the  source  of  the  odorous  emanations.  Thus  the 
form  of  the  response  is  here  the  distinctive  factor,  and  incidental 
to  this  feature  the  organs  of  smell  are  sensitive  to  far  smaller 
quantities  of  the  stimulating  substance  than  are  the  taste-buds. 
Parker  and  Stabler  have  shown  that  the  human  organ  of  smell 
is  sensitive  to  alcohol  at  a  dilution  24,000  times  greater  than  that 
necessary  to  stimulate  the  organs  of  taste  (see  p.  218). 

It  is  impossible  in  the  present  state  of  our  knowledge  to  frame 
adequate  definitions  of  all  the  senses  in  terms  of  any  one  of 
these  four  criteria  alone,  although  it  is  a  reasonable  hope  that 
this  may  at  some  future  time  be  attained.  Even  when  all  of 
these  criteria  are  taken  into  account,  it  is  by  no  means  easy  to 
determine  how  many  separate  senses  the  normal  human  being 


76  INTRODUCTION  TO  NEUROLOGY 

possesses.  Not  only  is  there  a  considerable  number  of  sense 
organs  not  represented  at  all  in  our  traditional  list  of  five  senses, 
but  several  of  these  five  are  complex.  Thus,  the  internal  ear 
includes  two  quite  distinct  organs — the  cochlea,  which  serves  as 
a  receptor  for  sounds,  and  the  labyrinth,  whose  semicircular 
canals  serve  as  the  chief  sense  organs  concerned  in  the  regula- 
tion of  bodily  position  and  the  maintenance  of  equilibrium,  func- 
tions which  are  quite  distinct  from  hearing.  The  skin,  too, 
serves  not  only  as  the  chief  organ  of  touch,  but  also  the  addi- 
tional functions  of  response  to  warm,  cold,  and  painful  impres- 
sions, besides  some  other  more  obscure  sensory  activities,  such 
as  tickle. 

An  acceptable  classification  of  the  sense  organs  or  receptors 
of  the  body  must  take  account  of  their  anatomical  relations,  of 
the  nature  of  the  physical  or  chemical  forces  which  serve  as  the 
adequate  stimufi,  of  the  subjective  qualities  which  we  experience 
upon  their  excitation,  and  of  the  character  of  the  physiological 
responses  which  commonly  follow  their  stimulation.  The  last 
point  has  been  too  much  neglected. 

In  fact,  the  most  fundamental  division  of  the  nervous  sys- 
tem which  we  have,  cutting  down  through  the  entire  bodily 
organization,  is  based  upon  this  physiological  criterion.  From 
this  standpoint  we  divide  the  nervous  organs  into  two  great 
groups:  (1)  a  somatic  group  pertaining  to  the  body  in  general 
and  its  relations  with  the  outer  environment,  and  (2)  a  visceral, 
splanchnic,  or  interoceptive  group.  The  latter  group  comprises 
the  nerves  and  nerve-centers  concerned  chiefly  with  digestion, 
respiration,  circulation,  excretion,  and  reproduction.  These  are 
intimately  related  with  the  sympathetic  nervous  system  and 
those  parts  of  the  central  nervous  system  directly  connected 
therewith,  though  the  more  highly  specialized  members  of  this 
group  are  independent  of  the  sympathetic  system.  The  somatic 
group  comprises  the  greater  part  of  the  brain  and  spinal  cord  and 
the  cranial  and  spinal  nerves,  or,  briefly,  the  cerebro-spinal  ner- 
vous system  as  distinguished  from  the  sympathetic  system  (see 
p.  225).  This  is  the  mechanism  by  which  the  body  is  able  to  ad- 
just its  own  activities  directly  in  relation  to  those  of  the  outside 
world— to  procure  food,  avoid  enemies,  and  engage  in  the 
pursuit  of  happiness. 


THE  RECEPTORS  AND  EFFECTORS  77 

The  organs  belonging  to  each  of  these  two  groups  do  much  of 
their  work  independently  of  the  other  group,  i.  e.,  visceral  stimuli 
call  forth  visceral  responses  and  external  or  somatic  stimuli 
call  forth  somatic  responses.  Nevertheless,  the  two  groups  of 
organs  are  by  no  means  entirely  independent,  for  external  excita- 
tions may  produce  strong  visceral  reactions,  and  conversely. 
Thus,  the  sight  of  luscious  fruit  (exteroceptive  stimulus)  natu- 
rally calls  forth  movements  of  the  body  (somatic  responses)  to  go 
to  the  desired  object  and  seize  it.  But  if  one  is  hungry,  the 
mouth  may  water  in  anticipation,  a  purely  visceral  response. 
On  the  other  hand,  the  strictly  visceral  (interoceptive)  sensation 
of  hunger  is  apt  to  set  in  motion  the  exteroceptive  reactions 
necessary  to  find  a  dinner. 

Sherrington,  whose  analysis  with  some  modifications  is  here 
adopted,  recognizes  three  types  of  sense  organs  or  receptors: 
(1)  the  inter oceptors,  or  visceral  receptive  organs,  which  respond 
only  to  stimulation  arising  within  the  body,  chiefly  in  connection 
with  the  processes  of  nutrition,  excretion,  etc.;  (2)  the  extero- 
ceptors,  or  somatic  sense  organs,  which  respond  to  stimulation 
arising  from  objects  outside  the  body;  (3)  the  proprioceptors,  a 
system  of  sense  organs  found  in  the  muscles,  tendons,  joints, 
etc.,  to  regulate  the  movements  called  forth  by  the  stimulation 
of  the  exteroceptors.  This  third  group  is  really  subsidiary 
to  the  somatic  group,  or  exteroceptors,  and  will  be  considered 
more  in  detail  below. 

The  proprioceptive  sense  organs  are  deeply  embedded  in  the 
tissues  and  are  typically  excited  by  those  activities  of  the  body 
itself  which  arise  in  response  to  external  stimulation.  The 
proprioceptors  then  excite  to  reaction  the  same  organs  of  re- 
sponse as  the  exteroceptors  and  regulate  their  action  by  reinforce- 
ment or  by  compensation  or  by  the  maintenance  of  muscular 
tone.  All  reactions  concerned  with  motor  coordination,  with 
maintenance  of  posture  or  attitude  of  the  body,  and  with 
equilibrium  involve  the  proprioceptive  system. 

The  important  point  to  bear  in  mind  here  is  that  stimulation 
of  the  visceral  sense  organs  typically  calls  forth  visceral  responses, 
i.  €.,  adjustments  wholly  within  the  body,  while  stimulation  of 
the  somatic  (exteroceptive)  sense  organs  typically  calls  forth 
somatic  responses,  i.  e.,  a  readjustment  of  the  body  as  a  whole 


78  INTRODUCTION  TO   NEUROLOGY 

with  reference  to  its  environment.  This  is  a  very  fundamental 
distinction.  These  two  functions  are  quite  diverse  and  the 
organization  of  these  two  parts  of  the  nervous  system  shows  cor- 
responding structural  differences. 

The  internal  adjustments  of  the  visceral  systems  are  effected 
by  a  nicely  balanced  mechanism  of  local  and  general  reflexes  so 
arranged  that  most  of  their  work  is  done  quite  mechanically  and 
unconsciously.  The  taking  of  food  and  its  preliminary  mastica- 
tion are  generally  voluntary  acts  whose  various  processes  are — 
or  may  be — controlled  at  will.  But  once  the  food  has  passed  into 
the  esophagus,  the  further  work  of  swallowing,  digestion,  and 
assimilation  is  no  longer  under  direct  control.  The  presence  of 
a  morsel  of  food  in  the  upper  part  of  the  esophagus  excites  the 
muscular  movements  necessary  for  the  completion  of  the  act  of 
swallowing,  which  no  act  of  will  can  prevent  or  modify.  In  fact, 
any  attempt  at  conscious  interference  or  regulation  is  apt  to 
result  in  an  incoordination  of  the  movements  involved,  and 
sputtering  or  gagging  may  result. 

The  mechanisms  involved  in  these  processes  are  inborn  and 
require  no  practice  for  their  perfect  performance.  They  are 
innate,  invariable,  and  essentially  similar  in  all  members  of  a 
race  or  species.  They  are,  moreover,  nicely  adapted  to  the 
mode  of  life  characteristic  of  the  species.  In  a  carnivorous  ani- 
mal the  whole  physiological  machinery  of  nutrition  is  different 
from  that  of  a  herbivorous  animal.  These  physiological  and 
structural  peculiarities  by  which  each  species  of  animal  is 
adapted  to  its  mode  of  life  have  been  brought  about  by  natural 
selection  and  other  evolutionary  factors.  This  is  not  absolutely 
true  of  all  visceral  actions;  some  are  acquired  and  modifiable. 
But  as  a  general  rule  this  is  their  type. 

Some  of  the  somatic  actions  are  likewise  innate  and  relatively 
fixed  in  character.  This  is  true  of  most  of  the  proprioceptive 
reactions  and  of  many  of  the  exteroceptive  as  well.  Fish  can 
swim  as  soon  as  they  are  hatched;  chicks  just  out  of  the  shell  have 
an  instinctive  tendency  to  peck  at  all  small  objects  on  the  ground. 
But  in  most  of  these  cases  (of  which  innumerable  instances 
might  be  cited)  some  practice  is  necessary  before  perfect  re- 
sponses are  attained;  and  a  very  large  proportion  of  the  extero- 
ceptive acts  are  not  innate,  but  acquired  by  long  and  often  ardu- 


THE  RECEPTORS  AND  EFFECTORS  79 

ous  experience.  In  higher  vertebrates,  as  a  rule,  all  but  the 
simplest  and  most  elementary  exteroceptive  activities  are  indi- 
vidually acquired,  variable,  non-hereditary,  plastic  behavior 
types.  The  elements  of  which  these  acts  are  made  up  are,  of 
course,  necessarily  present  in  the  inherited  reflex  pattern;  but 
the  pattern  according  to  which  these  elements  are  combined  is 
not  wholly  predetermined  in  the  hereditary  organization  of  the 
species  (pp.  31,  301). 

With  these  principles  in  mind,  let  us  now  undertake  an  anal- 
ysis of  the  human  receptors  and  of  the  nervous  end-organs  re- 
lated to  their  effectors,  or  organs  of  response.  The  following  list 
is  by  no  means  complete  and  is  in  some  parts  merely  provisional. 

I.     SOMATIC  RECEPTORS 

These  are  concerned  with  the  adjustment  of  the  body  to  external  or 
environmental  relations. 

A.  The  Exteroceptive  Group 

The  sense  organs  of  this  group  are  stimulated  by  objects  outside  the 
body  and  tjiDically  call  forth  reactions  of  the  whole  body,  such  as  locomo- 
tion, or  of  its  parts,  so  as  to  change  the  relation  of  the  body  to  its  environ- 
ment. This  group  includes  a  system  of  general  cutaneous  sense  ojgans, 
some  organs  of  deep  sensibility,  and  some  of  the  higher  sense  organs.  The 
cutaneous  exteroceptors  comprise  a  very  complex  system  whose  anah'sis 
has  proved  verj^  difficult.  The  conclusions  presented  in  the  paragraphs 
which  follow  are  based  chiefly  upon  the  observations  of  von  Frey,  Henry 
Head,  and  Trotter  and  Davies.  The  correlation  of  the  data  of  physiological 
experiment  with  the  anatomical  structm-e  of  the  cutaneous  end-organs  is 
still  somewhat  problematical  and  the  assignment  of  end-oxgans  here  to  the 
various  cutaneous  senses  should  be  regarded  as  provisional  rather  than  as 
demonstrated. 

1.  Organs  of  Touch  and  Pressure.— ^These  fall  ixito  two  groups,  those 
for  deep  sensibihty  (pressm-e)  and  those  for  cutaneous  sensibiHty  (touch). 
The  deep  pirssure  sense  is  served  by  nerve-endings  throughout  the  tissues 
of  the  bodj^  and  is  preserved  intact  after  the  loss  of  all  cutaneous  nerves. 
Most  of  the  functions  of  the  deep  sensory  nerves  belong  to  the  propriocep- 
tive and  interoceptive  series  (see  below) ,  but  some  exteroceptive  iunctions 
are  here  present  also.  The  latter  are  probably  related  chiefly  to  the 
Pacinian  corpuscles  and  similar  encapsulated  end-organs.  The  Pacinian 
corpuscle  has  a  central  nerve-fiber  enclosed  in  a  firm  lamellated  connective- 
tissue  sheath  (Fig.  22).  By  these  end-organs  relatively  coarse  pressure 
may  be  discriminated  and  localized  (exteroceptive  fimction),  and  movements 
of  muscles  and  joints  can  be  recognized  (proprioceptive  function).  The 
sensory  fibers  concerned  with  the  deep  pressure^ense^are  distributed  through 
the  muscular  branches  of  the  spinal  nerves  in  company  with  the  motor 
fibers.     The  point  stimulated  can  be  localized  with  a  fair  degi-ee  of  accuracy, 


80 


INTRODUCTION   TO   NEUROLOGY 


but  there  is  no  discrimination  of  two  compass  points  applied  simultaneously 
to  the  overlying  skin.  The  two  points  will  appear  as  one  stimulus,  even 
when  widely  separated. 

The  cutaneous  organs  of  tactile  sensibility  are  of  several  kinds,  whose 
precise  functions  are  still  obscure.  There  are  two  principal  groups  of  these, 
those  arranged  in  the  hair  bulbs  at  the  roots  of  the  hairs  and  those  on  the 
hairless  parts,  such  as  the  hps,  the  palms  of  the  hands,  and  the  soles  of  the 
feet.  The  latter  are  more  highly  differentiated  endings  and  are  organs  of 
the  most  refined  active  touch. 

Most  of  the  surface  of  the  body  is  more  or  less  hairy,  though  many  of 
these  hairs  may  be  so  fine  as  to  escape  observation.     The  hairs  are  the  most 


Fig.  22. — Pacinian  corpuscles  from  the  peritoneum  of  a  cat.     (After  Sala, 
from  Bohm-Davidoff-Huber's  Histology.) 


important  sources  of  excitation  of  the  first  group  of  cutaneous  sense  organs, 
and  the  sensitiveness  of  the  hair-clad  parts  is  greatly  reduced  after  the  hair 
is  shaved.  The  threshold  of  excitation  to  touch  of  the  skin  about  the  base 
of  a  hair  is  from  three  to  twelve  times  higher  than  that  of  a  similar  excita- 
tion applied  to  the  hair  itself.  The  innervation  of  the  hair  bulbs  is  very 
complex  and  varies  greatly  for  different  animals  and  for  the  different  kinds 
of  hairs  on  the  same  body,  so  that  no  general  description  is  possible. 

Miss  Vincent  has  shown  that  the  large  vibrissse  of  the  rat  receive  their 
nerve-supply  from  two  sources.     A  large  nerve  bundle  pierces  the  deep 


THE  RECEPTORS  AND  EFFECTORS 


81 


layer  of  the  skin  (dermis)  in  the  lower  part  of  the  hair  bulb,  spreads  out 
over  the  inner  hair  follicle  in  a  heavy  plexus,  and  terminates  chiefly  in  a 
mantle  of  touch  cells,  resembling  Merkel's  corpuscles  (see  Fig.  26),  in  the 
outer  root  sheath  all  over  the  follicle.  A  second  nerve  supply  comes  from 
the  dermal  plexus  of  the  skin,  from  which  branches  run  down  and  form  a 
nerve  ring  about  the  neck  of  the  follicle.  Experimental  studies  show  that 
these  hairs  are  very  important  not  only  as  general  tactile  organs,  but 


Fig.  23. — Nerve-endings  about  a  large  hair  from  the  dog.  The  nerve- 
fibers  are  shown  in  black  surrounding  the  hair  shaft,  the  straight  fibers 
at  h  and  the  circular  fibers  at  c.  (After  Bonnet,  from  Barker's  Nervous 
System.)^ 


specifically  as  aids  in  locomotion  and  equilibration.  The  ordinary  hairs  of 
man  and  other  mammals  have  three  forms  of  specific  nerve-endings  in  addi- 
tion to  various  forms  of  terminal  arborizations  in  the  surrounding  tissues: 
(1)  straight  and  often  forked  endings  running  parallel  with  the  base  of  the 
hair;  (2)  circular  fibers  forming  a  plexiform  ring  around  the  root  of  the 
hair  external  to  the  straight  endings;  and  (3)  leaf -like  nerve-endings  associ- 
ated with  special  cells  resembling  i\I('rk(>rs  corpuscles.  Figure  23  illustrates 
the  first  and  second  types  of  these  endings. 

6 


82 


INTRODUCTION   TO    NEUROLOGY 


Under  the  hairless  parts  of  the  skin  there  are  special  tactile  bodies,  such 
as  Meissner's  corpuscles.  These  are  generally  found  in  the  deep  layer  of 
the  skin  (dermis)  and  in  the  underlying  tissues,  either  as  free  skein-like 
terminal  arborizations  of  cutaneous  nerves  or  as  similar  more  elaborate 
endings  enclosed  in  connective-tissue  capsules.  Figures  24  and  25  illustrate 
the  most  highly  differentiated  form  of  these  endings,  the  Meissner  cor- 
puscles. Merkel's  corpuscles  (Fig.  26)  are  probably  simpler  organs  of  this 
system. 


_;.  I,  Stratum 
corneum 


TT-Stratum  lucidum 

Stratum 

^S^S^^T"  granulosum 

Stratum 
mucosum 

Stratum 
erminatmira 

Nervous 
papilla  of 
corium 


Blood-vessels 
and  nerves 


Fig.  24. — Section  through  the  human  skin,  illustrating  the  four  layers 
of  the  epidermis  and  the  papillae  of  the  dermis  or  corium.  A  corpuscle  of 
Meissner  is  seen  within  one  of  the  dermal  papillae.  (From  Cunningham's 
Anatomy.) 


All  forms  of  cutaneous  sensibility  (touch,  temperature,  and  pain)  when 
studied  physiologically  are  found  to  be  localized  in  small  areas  or  sensory 
spots,  each  of  which  has  a  specific  sensibility  to  one  only  of  the  cutaneous 
sensory  qualities.  The  intervening  parts  of  the  skin  are  insensitive.  An 
immense  amount  of  physiological  and  clinical  observation  has  been  devoted 
to  the  analysis  of  cutaneous  sensibility,  including  the  experimental  division 


THE  RECEPTORS  AND  EFFECTORS 


83 


Fig.  25. — The  details  of  the  nerve-endings  in  a  Meissner  corpuscle  from 
the  human  skin.  Only  the  outline  of  the  corpuscle  is  showTi,  within  which 
the  terminals  of  the  nerve-fiber  form  a  complex  skein.  (After  Dogiel,  from 
Bohm-Davidoff-Huber's  Histology.) 


Fig.  26. —  Merkel's  corpuscles  or  tactile  disks  from  the  skin  of  the  pig's 
snout.  The  nerve-fiber,  n,  branches,  and  each  division  ends  in  an  expanded 
disk,  7/1,  which  is  attached  to  a  modified  cell  of  the  epidermis,  a.  The  un- 
modified cells  of  the  epidermis  are  shown  at  c.     (From  Ranvier.) 


84  INTRODUCTION  TO  NEUROLOGY 

of  cutaneous  nerves  in  their  own  bodies  by  Head,  Trotter,  and  Davies  for 
the  purpose  of  studying  more  critically  the  distribution  of  the  various 
sensory  functions  in  and  around  the  anesthetic  areas  produced  by  the 
injuries  and  the  phenomena  accompanying  the  restoration  of  these  functions 
during  the  regeneration  of  the  nerves.  But  general  agreement  has  not  yet 
been  reached  on  aU  questions. 

Head  and  his  colleagues  are  of  the  opinion  that  all  forms  of  cutaneous 
sensibility  (touch,  temperature,  and  pain)  are  grouped  in  two  series,  each 
served  by  different  nerve-fibers  and  end-organs;  these  he  terms  "proto- 
pathic"  and  "epicritic"  sensibility.  Protopathic  sensibility  is  subjectively 
general  diffuse  sensibiUty  of  a  primitive  form.  Its  sense  organs  are  arranged 
in  definite  spots,  and  yet  these  sensations  have  no  clear  local  reference  or 
sign;  that  is,  the  spot  stimulated  cannot  be  accurately  localized.  There  are 
separate  spots  for  touch,  heat,  cold,-  and  pain;  these  spots  being  generally 
grouped  near  the  hair  bulbs.  In  fact,  the  hairs  are  the  most  important 
tactile  organs  of  this  system  and  the  other  sense  qualities  belonging  here  are 
intimately  associated  with  the  roots  of  the  hairs.    Epicritic  sensibility  is 


Fig.  27. — End-bulb  of  Krause  from  the  conjunctiva  of  man.  The 
nerve-ending  forms  a  globular  skein  within  a  delicate  connective-tissue 
capsule.     (After  Dogiel.) 

a  more  refined  sort  of  discrimination,  and  is  regarded  as  a  later  evolutionary 
tjTJe.  It  includes  light  touch,  on  the  hairless  parts  of  the  body  particularly, 
and  the  discrimination  of  the  intermediate  degrees  of  temperature.  Cuta- 
neous localization  and  the  discrimination  of  the  distance  between  two  points 
simultaneously  stimulated  (the  "compass  test")  are  functions  of  this  sys- 
tem; but  pain  sensibihty  is  not  included,  this  being  wholly  protopathic. 

Trotter  and  Davies  repeated  some  of  Head's  experiments  and,  while 
confirming  most  of  his  observations,  they  were  led  to  somewhat  different 
conclusions.  They  do  not  regard  the  protopathic  and  epicritic  series  as 
served  by  distinct  systems  of  nerves,  but  as  different  physiological  phases  of 
the  same  systems  of  nerve-fibers  and  end-organs. 

2.  End-organs  for  Sensibility  to  Cold. 

3.  End-organs  for  Sensibility  to  Heat. — Physiological  experiment 
shows  that  warmth  and  cold  are  sensed  by  different  parts  of  the  skin  (the 
warm  spots  and  the  cold  spots  respectively),  and  Head  is  of  the  opinion  that 
each  of  these  types  of  sensibility  may  be  present  in  an  epicritic  and  a  proto- 
pathic form.  What  end-organs  are  involved  here  is  by  no  means  certain. 
The  margin  of  the  cornea  was  found  by  von  Frey  to  be  sensitive  to  pain  and 


THE  RECEPTORS  AND  EFFECTORS 


85 


cold  onlj'.  The  free  nerve-endings  found  here  he  assumes  to  be  pain  recep- 
tors and  the  end-bulbs  of  Krause  (Fig.  27)  to  be  cold  receptors,  ^y  an 
analogous  argument  he  assumes  that  the  "genital  corpuscles"  of  Dogiel  and 
some  similar  endings  widely  distributed  in  the  skin  are  warmth  receptors. 
By  some  other  physiologists  these  types  of  corpuscles  are  regarded  as  belong- 
ing to  the  tactile  system.  Stimulation  of  the  somatic  nerves  of  deep  sensi- 
bility causes  no  temperature  sensations.  (For  temperature  sensations  in  the 
viscera  see  p.  242.) 

4.  End-organs  for  Pain. — Some  phj^siolo- 
gists  believe  that  there  are  separate  nerve- 
endings  for  pain;  others  regard  pain  as  a 
quality  which  may  be  present  in  any  sense, 
and  not  as  itself  a  true  sensation  (pp.  249 
ff.).  The  free  nerve-endings  among  the  cells 
of  the  epidermis  are  regarded  by  von  Frey 
as  the  pain  receptors,  because  these  endings 
alone  are  present  in  some  parts  of  the  body 
where  susceptibihty  to  pain  is  the  only  sense 
quaUty  present,  such  as  the  dentin  and  pulp 
of  the  teeth  (Fig.  28),  the  cornea,  and  the 
tympanic  membrane  of  the  ear  (J.  G.  Wilson). 

Similar  endings  are  found  throughout  the 
epidermis  (Fig.  29)  and  in  many  deep  struc- 
tures. The  nerves  of  deep  sensibility  of  the 
somatic  sensory  type  may  also  carry  painful 
impressions.  (For  visceral  pain  see  pp.  243, 
250.)  According  to  Head,  cutaneous  pain  is 
wholly  of  protopathic  type,  and  in  case  of  in- 
jury to  the  peripheral  nerves  it  disappears 
and  reappears  in  regeneration  simultaneously 
with  the  protopathic  type  of  tactile  and  tem- 
perature sensation.  This  cutaneous  pain  is 
not  accurately  locaUzable  unless  epicritic  cu- 
taneous sensibility  is  also  present. 

5.  End-organs  of  General  Chemical  Sen- 
sibility.— In  man  this  type  of  sensibility  is 
found  only  on  moist  epitheUal  surfaces,  such 
as  the  mouth  cavity;  but  in  fishes  it  may  be 
present  over  the  entire  surface  of  the  body. 
The  sense  organ  is  probably  the  free  nerve 
terminals  among  the  cells  of  the  epithelium, 
never  special  sense  organs  hke  taste-buds, 
for  these  when  present  in  the  skin  belong 
to  a  quite  different  system.  Coghill  has 
recently  showm  that  the  supposed  sensitivity  of  the  amphibian  skin  to  acids 
is  really  due  to  a  destructive  action  of  the  reagents  upon  the  epithelium,  and 
the  entire  question  of  diffuse  chemical  sensibility  requires  further  study. 

6.  Organs  of  Hearing. — The  stimulus  is  material  vibrations  whose 
frequency  ranges  from  30  to  30,000  per  second  (see  p.  70).  The  receptor  is 
the  spiral  organ  (organ  of  Corti)  in  the  cochlea  of  the  ear  (see  p.  197),  and 
perhaps  also  the  sensory  spots  in  the  saccule  and  utricle.  There  are  two 
forms  of  auditory  sensations:  (1)  noise,  stimulated  by  sound  concussions  or 
irregular  mixtures  of  aerial  vibrations;  (2)  tone,  stimulated  by  sound  waves 
or  periodic  aerial  vibrations. 


Fig.  28. — Longitudinal 
section  of  a  tooth  of  a  fish, 
Gobius,  showing  nerve  ter- 
minals: d,  Dentin;  7i, 
nerve-fibers  entering  the 
cavity  of  the  dentin  and 
ending  free.  (After  Ret- 
zius,  from  Barker's  Ner- 
vous System.) 


86 


INTRODUCTION   TO    NEUROLOGY 


7.  Organs  of  Vision. — The  stimulus  is  ethereal  vibrations  ranging  be- 
tween 400,000  billions  and  800,000  billions  per  second.  Here  also  there 
are  two  forms:  (1)  brightness,  stimulated  by  mixed  ethereal  vibrations; 
(2)  color,  stiin.ulated  by  simpler  ethereal  vibrations.  (On  the  structure  of 
the  eye  and  its  connections  see  p.  204.) 


Fig.  29. — ^Transverse  section  through  the  skin  of  the  ear  of  a  white 
mouse.  The  dotted  line  marks  the  lower  border  of  the  epidermis:  a,  Hori- 
zontal nerve-fibers;  h,  bifurcation  of  nerve-fibers;  fn,  cutaneous  nerve- 
fibers.     (After  Van  Gehuchten,  from  Barker's  Nervous  System.) 

8.  Organs  of  Smell. — This  sense  has  both  exteroceptive  and  intero- 
ceptive qualities,  the  latter  being  apparently  the  more  primitive.  (See 
pp.  75,  91,  and  21S.) 


B..  The  Proprioceptive  Group 

These  sense  organs  are  contained  within  the  skeletal  muscles,  joints,  etc., 
and  are  stimulated  by  the  normal  functioning  of  these  organs,  thus  report- 
ing back  to  the  central  nervous  system  the  exact  state  of  contraction  of  the 
muscle,  flexion  of  the  joint,  and  tension  of  the  tendon.  Cutaneous  sensi- 
bility may  also  participate  in  these  reactions,  which  are  generally  uncon- 
sciously performed. 

9.  End-organs  of  Muscular  Sensibility. — The  organ  is  a  series  of 
nerve-endings  among  special  groups  of  muscle-fibers  known  as  muscle 
spindles.  These  endings  are  usually  spirally  wound  around  their  muscle- 
fibers  and  are  stimulated  by  the  contraction  of  the  muscle  (Fig.  30). 


THE  RECEPTORS  AND  EFFECTORS 


87 


As  we  shall  see  below  (p.  92),  the  muscles  are  classified  for  our  purposes 
into  three  groups:  (1)  somatic  muscles  (the  striated  skeletal  muscles);  (2) 
general  visceral  muscles  (generally  unstriated  and  involuntar}-) ;  and  (3) 
special  visceral  muscles  of  the  head  which  are  striated  and  voluntary.  The 
first  and  third  of  these  groups  receive  their  motor  innervation  from  cere- 
bro-spinal  nerves;  the  second,  from  sympathetic  nerves.    The  classification 


Fig.  30. — ^Muscle  spindle  from  the  muscles  of  the  foot  of  a  dog.  Three 
muscle-fibers  are  shown  and  three  sensory  nerve-fibers,  which  enter  the 
muscle  spindle,  branch,  and  wind  spirally  around  the  muscle-fibers  (a,  b). 
A  sympathetic  nerve-fiber  (Sy.n.)  also  enters  the  muscle  spindle.  (After 
Huber  and  DeWitt,  from  Barker's  Nervous  System.) 

of  the  nerves  of  muscle  sense  related  respectively  to  these  three  groups  of 
muscle  offers  some  difficulties.  The  striated  muscles  of  the  first  and  third 
groups  are  physiologically  similar  in  that  they  act  in  general  in  response  to 
exteroceptive  stimuli  and  they  may  be  voluntarily  excited,  while  the  visceral 
muscles  of  the  second  gi'oup  are  generalh'  stimulated  by  interoceptive  stim- 


Fig.  31. — A  teased  preparation  of  a  tendon  of  a  small  muscle  from  a 
rabbit,  showing  the  endings  of  the  nerve-fibers  of  tendon  sensibility,  each 
of  which  spreads  out  widely  over  the  surface  of  the  tendon.  (After  Huber 
and  DeWitt,  from  the  Journal  of  Comparative  Neurology.) 


uli  and  their  functions  are  usually  involimtary.  I  have,  accordingly,  some- 
what arbitrarily  regarded  the  sensory  nerves  of  the  first  and  third  groups 
of  muscles  as  proprioceptors  and  those  of  the  second  group  as  interoceptors. 
10.  End-organs  of  Tendon  Sensibility. — Nerve-endings  are  spread 
out  over  the  surface  of  tendons  and  are  .-stimulated  by  stretching  the  tendon 
during  muscular  contraction  (Fig.  31). 


88 


INTRODUCTION   TO    NEUROLOGY 


11.  End-organs    of    Joint   Sensibility. — Nerve-endings  found  in  the 
joints- and  the  surrounding  tissues  are  stimulated  by  bending  the  joint,  and 


Fig.  32. — Diagram  of  the  relations  of  a  fiber  of  the  vestibular  branch 
of  the  auditory  nerve  and  its  mode  of  termination  in  the  semicircular 
canal:  co,  The  central  nervous  system;  fz,  non-nervous  supporting  cell  of 
the  semicircular  canal ;  hz,  hair  cell,  one  of  the  receptor  cells  of  the  sensory 
surface;  sn,  axon  of  the  vestibular  neuron;  sz,  cell  body  of  the  vestibular 
neuron.     (After  Retzius,  from  Barker's  Nervous  System.) 

report  back  to  the  central  nervous  system  the  degree  of  flexion  of  the  joint. 
The  chief  end-organs  are  probably  Pacinian  corpuscles  (see  Fig.  22). 


THE  RECEPTORS  AND  EFFECTORS  89 

12.  Organs  of  static  and  equilibratory  sensation  arising  from 
stimulation  of  the  semicircular  canals  of  the  internal  ear  (Fig.  32).  This  is 
the  most  highly  specialized  member  of  the  proprioceptive  group  and  acts 
in  conjunction  with  all  of  the  other  somatic  senses  to  maintain  equilibrium, 
posture,  and  the  tone  of  the  muscular  system  (see  p.  189).  The  eyes  and 
most  of  the  other  exteroceptive  sense  organs,  so  far  as  they  act  in  the  way 
just  suggested,  also  serve  as  proprioceptors. 


II.    VISCERAL  RECEPTORS 

The  visceral  or  interoceptive  senses  fall  into  two  well-defined  groups: 
First,  the  general  visceral  systems  are  without  highly  specialized  end-organs 
and  are  innervated  through  the  sympathetic  nervous  system.  Their  reac- 
tions are  chiefly  unconsciously  performed.  Second,  the  special  visceral 
senses  are  provided  with  highly  developed  end-organs  which  are  in- 
nervated directly  from  the  brain  without  any  connection  with  the  sympa- 
thetic nervous  system.  The  special  visceral  sense  organs  may  in  some 
cases  serve  as  exteroceptors  as  well  as  interoceptors.  Their  reactions 
may  be  conscious  and  voluntary. 

A.  General  Visceral  Group 

Many  of  the  sensations  of  this  group  are  obscure  and  a  number  of  excito- 
motor  and  excito-glandular  reactions  may  be  included  here  which  never 
come  into  clear  consciousness,  particularly  those  concerned  with  nutrition, 
excretion,  and  vasomotor  adjustments.  The  number  of  these  reactions 
might  be  considerably  increased;  for  further  discussion  of  these  reflexes 
see  p.  234. 

13.  Organs  of  Hunger. — The  stimulus  is  strong  periodic  contractions 
of  the  muscles  of  the  stomach.  Hunger  is  apparently  a  variety  of  muscle 
sense,  but  other  factors  are  also  present  (see  p.  240). 

14.  Organs  of  Thirst. — The  specific  stimulus  here  is  probably  a  dry- 
ing of  the  pharyngeal  mucous  membrane,  together  with  more  general 
conditions. 

15.  Organs  of  Nausea. — ^The  stimulus  is  probably  an  antiperistaltic 
reflex  in  the  digestive  tract  (see  p.  243). 

16.  Organs  giving  rise  to  respiratory  sensations,  sufTocation,  etc.  (see 
p.  235). 

17.  Organs  giving  rise  to  circulatory  sensations,  flushing,  heart  panics, 
etc.  (see  p.   234). 

18.  Organs  giving  rise  to  sexual  sensations. 

19.  Organs  of  sensations  of  distention  of  cavi.ties,  stomach,  rectum, 
bladder,  etc.     This  is  a  variety  of  muscle  sense. 

20.  Organs  of  visceral  pain  (see  pp.  243,  250). 

21.  Organs  of  obscure  abdominal  sensations  associated  with  strong 
emotions  of  fright,  anger,  affection,  etc.,  characterized  (probably  correctly) 
by  the  ancients  by  such  expressions  as  "yearning  of  the  bowels,"  etc.  The 
stimulus  is  probably  a  tonic  contraction,  of  the  unstriped  visceral  muscula- 
ture. 

The  nerve-endings  of  the  general  visceral  receptors  are  generally  either 
simple  terminals  in  the  visceral  muscles  or  free  arborizations  in  or  under  the 
various  mucous  surfaces,  without  the  development  of  specialized  accessory 


90 


INTRODUCTION   TO    NEUROLOGY 


cells  to  form  differentiated  sense  organs.  Figure  33  illustrates  a  sensory  end- 
ing in  the  mucous  membrane  of  the  esophagus,  and  Fig.  34  types  of  nerve- 


Fig.  33. — Free  nerve-endings  in  the  mucous  membrane  of  the  esoph- 
agus of  a  cat.  (After  DeWitt,  from  Wood's  Reference  Handbook  of  the 
Medical  Sciences.) 


Fig.  34. — Nerve-endings  in  the  mouth  epithehum  of  the  frog:  A,  From 
sensory  papilla  of  the  tongue;  B,  cyUnder  cells;  C,  isolated  rod  cell;  D,  upper 
part  of  papilla;  E,  ciliate  cells  of  palate.  (After  Bethe,  from  Wood's  Refer- 
ence Handbook  of  the  Medical  Sciences.) 


endings  upon  epithelial  cells.  The  nerve-endings  in  the  visceral  muscles 
are  very  sunple  (see  Figs.  37  and  38)  and  the  separation  of  sensory  from 
motor  endings  here  has  not  been  effected. 


THE  RECEPTORS  AND  EFFECTORS 


91 


B.  Special  Visceral^  Group. 

22.  Organs  of  Taste. — These  are  excited  by  chemical  stimulation  of 
taste-buds  on  the  tongue  and  pharynx  by  sweet,  sour,  salty,  or  bitter  sub- 
stances. In  man  this  is  a  strictly  interoceptive  sense;  but  in  some  fi.shes 
taste-buds  are  scattered  over  the  outer  body  surface  in  addition  to  the  mouth 
cavity,  and  thus  may  serve  as  exteroceptors  also.  The  organ  is  a  flask- 
shaped  collection  of  specialized  epithelial  cells  of  two  sorts,  supporting  and 
specific  sensory  elements  (Fig.  35).  There  is  a  double  innervation,  partly 
by  perigemmal  fibers  whose  endings  surround  the  bud,  and  partly  by  intra- 
gemmal  fibers  which  penetrate  the  bud  and  arborize  in  intimate  relation 
with  the  specific  sensory  cells. 

23.  Organs  of  Smell. — These  are  excited  by  chemical  stimulation  of  the 
specific  olfactory  mucous  membrane  of  the  nose.    The  number  of  substances 


Fig.  35. — Taste-bud  from  the  side  wall  of  a  circmn vallate  papilla  of  the 
tongue:  a,  Taste-pore;  b,  nerve-fibers,  some  of  which  enter  the  taste-bud 
(intragemmal  fibers),  while  others  end  freely  in  the  surrounding  epithelium 
(perigemmal  fibers).     (After  Merkel-Henle.) 


which  maj^  act  as  stimuli  is  greater  than  in  the  case  of  taste-buds,  the  num- 
ber of  subjective  qualities  is  also  greater,  and  the  discrimination  threshold 
is  much  lower  (see  pp.  75  and  218).  The  peripheral  organ  of  smell  is  a 
specific  sensory  epithelium  within  the  nose,  whose  sensory  cells  give  rise 
directly  to  the  fibers  of  the  olfactory  nerve,  this  being  the  only  peripheral 
nerve  of  the  human  body  whose  fibers  arise  from  superficially  placed  cell 
bodies  (Fig.  36). 

That  the  olfactory  system  was  originally  an  interoceptive  sense  seems 
clear;  but  in  all  vertebrates  living  at  the  present  time, the  visceral  responses 
to  smell  are  less  important  than  the  somatic  reactions.  The  sense  of  smell 
is  the  leading  extcroccptor  in  most  lower  vertebrates,  and  this  function  has 
been  secondarily  derived  from  the  primary  visceral  function.  We  have  seen 
above  that  the  sense  of  taste  in  some  fi.shes  has  secondarity  acquired  extero- 
ceptive functions;  and  in  the  case  of  smell  this  secondary  change  has  been 
carried  still  further  until  the  exteroceptive  function  has  come  to  dominate 


&2 


IXTEODrCTIOX    TO    XEUEOLOGT 


Olfactoiy 
hails' 


.Olikctory 
halis 


Peripheral 

process 


Body  of 
-  cell  with 
nucleus 


Central 

prc-cess 


Fig.  36. — Cells  from  the  olfactory  mucous  membrane:  A  from  the  frog, 
B  and  C  from  man.  The  supportmg  cells  are  non-nervous.  The  oKactory 
hairs  of  the  oh'actory  cells  project  out  into  the  mucus  of  the  nose,  and  are 
probably  the  specific  receptors.  The  central  process  at  theba-e  oi  each 
olfactory  cell  is  prolonged  into  a  fiber  of  the  olfactory  nerve  not  shown 
in  the  figiu-e\  which  extends  inward  to  the  brain  (cf.  Fig.  104.  p.  217). 
(After  Schnlte  and  Brimn.) 

the  primitive  interoceptive,  though  the  latter  has  by  no  means  been  en- 
tirelv  obliterated. 


m.     SOMATIC  EFFECTORS 

24.  End-organs  on  Striated  Skeletal  Muscles. — This  "motor  end- 
plate"  is  a  complex  terminal  arborization  of  the  motor  nerve-fiber,  associ- 
ated with  an  elevated  granular  mass  of  protoplasm  and  a  collection  of 
nticlei  of  the  mtiscle-fiber  (see  Fig.  5,  id,  p.  40 ~i. 

The  somatic  mtiscles  whose  innervation  is  here  under  consideration  are 
derived  embryologically  from  the  somites,  or  primary  mesodermal  segments 
of  the  embryo,  while  the  visceral  muscles  have  a  different  origin.  They  are 
tmder  the  direct  control  of  the  will  and  are  concerned  chiefly  with  loco- 
motion or  other  movements  which  change  the  relations  of  the  body  to  its 
environment.  They  are  tj-pically  stunulated  to  action  tlu'ough  the  ex- 
teroceptive sense  organs.  They  make  up  the  bulk  of  the  musctilatm-e  of 
the  trimk  and  limbs  and  are  represented  in  the  head  only  in  the  external 
muscles  of  the  eyeball  and  a  part  of  the  mtiscles  of  the  tongue. 


THE    RECEPTORS    AND    EFFECTORS 
IV.    VISCERAL  EFFECTORS 


93 


25.  End-organs  on  the  Involuntary  Visceral  Muscles. — These  muscles 
may  be  unstriated  or  striated  (as  in  heart  musclej.     They  are  innervated 


■^*«s«^,^ 


Fig.  37. — Two  unstriated  involuntary  muscle-fibers,  showing  the  nerve- 
endings:  a,  Axon;  b.  its  termination;  n,  nucleus  of  the  smooth  muscle 
cell.     (After  Huber  and  DeWitt,  from  Barker's  Nervous  System.) 

through  the  sympathetic  nervous  system  and  tj-pically  by  a  chain  of  two 
neurons,  the  preganglionic  and  the  postganglionic  neurons  (see  p.  229). 


« 
• 


Fig.  38. — Three  striated  cardiac  muscle   cells,  with  their  nerve-endings. 
(After  Huber  and  DeWitt,  from  Barker's  Nervous  System.) 

The  body  of  the  preganglionic  neuron  Ues  in  the  central  ner\'0us  system  and 
its  axon  passes  out  into  the  sj-mpathetic  ner^^ous  system,  where  it  ends  in  a 
sympathetic  ganglion.  The  efferent  impulse  is  here  taken  up  by  a  post- 
ganglionic neuron,  whose  body  lies  in  the  s\"mpathetic  ganghon  in  question 


94  INTRODUCTION  TO  NEUROLOGY 

and  whose  axon  passes  onward  through  a  sympathetic  nerve  to  end  in  the 
appropriate  effector.  The  nerve-endings  of  this  system  are  simple  or 
branched  free  terminals  ending  on  the  surface  of  the  muscle-fiber  (Fig.  37) ; 
in  the  case  of  heart  muscle  the  fibers  usually  have  expanded  tips  (Fig.  38). 

26.  End-organs  on  Glands. — The  innervation  of  these  organs  is  in  most 
respects  similar  to  that  of  the  involuntary  muscles  last  described.  A  fine 
plexus  of  unmyeUnated  fibers  of  sympathetic  origin  envelops  the  smaller 
glands  and  pervades  the  larger  ones;  these  are  beheved  in  some  cases  to  be 
the  excito-glandular  fibers. 

27.  Special  Visceral  Motor  End-organs. — The  nerves  of  these  muscles 
have  no  connection  with  the  sympathetic  nervous  system.  These  effectors 
are  striated  muscles  which  may  act  under  the  direct  control  of  the  will. 
In  their  evolutionary  origin  they  are  derived  from  the  muscles  of  the  gills 
of  the  lower  vertebrates,  and  they  are  developed  embryologically  from  the 
ventral  unsegmented  mesoderm  and  not  from  the  primitive  mesodermal 
segments  which  give  rise  to  the  somatic  muscles.  They  are  found  only  in 
the  head  and  neck  and  their  nerve-endings  are  similar  to  those  of  the 
striated  muscles  of  the  somatic  series. 

Summary. — We  have  seen  that  the  chief  function  of  the  sense 
organs  is  to  lower  the  threshold  of  excitability  of  the  body  in 
definite  places  to  particular  kinds  of  stimulation,  and  thus  to 
effect  an  analysis  of  the  forces  of  nature  so  far  as  these  concern 
the  welfare  of  the  body.  The  nature  of  this  analysis  of  the  en- 
vironing energy  complex  was  illustrated  by  a  review  of  the  ways 
in  which  the  body  may  respond  to  different  kinds  of  vibrations. 
The  senses,  as  this  word  is  commonly  used,  were  distinguished 
by  four  criteria,  termed  briefly  the  psj^chological,  physical,  ana- 
tomical, and  physiological.  Then  followed  a  physiological  classi- 
fication of  the  receptors  and  effectors  of  the  human  body. 

Literature 

Barker,  L.F.  1901.  The  Nervous  System  and  Its  Constituent  Neurones, 
New  York. 

CoGHiLL,  G.  E.  1914.  Correlated  Anatomical  and  Physiological  Studies 
of  the  Growth  of  the  Nervous  System  of  Amphibia.  I.  The  Afferent  Sys- 
tem of  the  Trunk  of  Amblystoma,  Jour.  Comp.  Neur.,  vol.  xxiv,  pp.  161-233. 

VON  Frey,  M.  1897.  Untersuchungeh  uber  die  Sinnesfunctionen  der 
menschlichen  Haut,  Abhangl.  kgl.  sachs.  Gesellsch.,  Bd.  40  (Math.-Phys. 
Classe,  Bd.  23). 

Head,  H.,  Rivers,  W.  H.  R.,  and  Sherren,  J.  1905.  The  Afferent 
Nervous  System  from  a  New  Aspect,  Brain,  vol.  xxviii,  pp.  99-115. 

Herrick,  C.  Judson.  1903.  On  the  Morphological  and  Physiological 
Classification  of  the  Cutaneous  Sense  Organs  of  Fishes,  Amer.  Naturalist, 
vol.  xxxvii,  pp.  313-318. 

— .  1908.  On  the  Phylogenetic  Differentiation  of  the  Organs  of  Smell 
and  Taste,  Jour.  Comp.  Neur.,  vol.  xviii,  pp.  157-166. 

■ — .  1914.  End-organs,  Nervous,  Wood's  Reference  Handbook  of  the 
Medical  Sciences,  3d  ed.,  vol.  iv,  pp.  20-27,  New  York. 


THE  RECEPTORS  AND  EFFECTORS  95 

Hertz,  A.  F.  1911.  The  Sensibility  of  the  AHmentary  Canal,  London. 

HuBER,  G.  C.  1900.  Observations  on  Sensory  Nerve-fibers  in  Visceral 
Nerves  and  on  their  Modes  of  Terminating,  Jour.  Comp.  Neur.,  vol.  x, 
pp.  134-151. 

HuBER,  G.  C.,  and  DeWitt,  Lydia,  M.  A.  1897.  A  Contribution  on 
the  Motor  Nerve-endings  in  the  Muscle-spindles,  Jour.  Comp.  Neur.,  vol. 
vii,  pp.  169-230. 

— .  1900.  A  Contribution  on  the  Nerve  Terminations  in  Neuro-tendi- 
nous  End-organs,  Jour.  Comp.  Neur.,  vol.  x,  pp.  1.59-208. 

Parker,  G.  H.  1912.  The  Relation  of  Smell,  Taste,  and  the  Common 
Chemical  Sense  in  Vertebrates,  Jour.  Acad.  Nat.  Sci.,  Phila.,  2  Ser.,  vol. 
XV,  pp.  221-234. 

Parker,  G.  H.,  and  Stabler,  Eleanor  M.  1913.  On  Certain  Distinc- 
tions Between  Taste  and  Smell,  Amer.  Jour.  Physiol.,  vol.  xxxii,  pp.  230- 
240. 

Rivers,  W.  H.  R.,  and  Head,  H.  1908.  A  Human  Experiment  in  Nerve 
Division,  Brain,  vol.  xxxi,  p.  32.3. 

Sheldon,  R.  E.  1909.  The  Reactions  of  the  Dogfish  to  Chemical  Stim- 
uli, Jour.  Comp.  Neur.,  vol.  xix,  pp.  273-311. 

Sherrington,  C.  S.  1906.  The  Integrative  Action  of  the  Nervous  Sys- 
tem, New  York. 

Trotter,  W.,  and  Davies,  H.  M.  1909.  Experimental  Studies  in  the 
Innervation  of  the  Skin,  Jour,  of  Physiol.,  vol.  xxxviii,  pp.  134-246. 

Vincent,  Stella  B.  1913.  The  Tactile  Hair  of  the  White  Rat,  Jour. 
Comp.  Neur.,  vol.  xxiii,  pp.  1-38. 

— .  1913a.  The  Function  of  the  Vibrissse  in  the  Behavior  of  the  White 
Rat,  Behavior  Monographs,  vol.  i.  No.  .5,  pp.  7-81. 

Watson,  J.  B.  191.5.  Behavior,  An  Introduction  to  Comparative  Psy- 
chology, Chapters  XI-XIV,  New  York. 

Wilson,  J.  G.  1911.  The  Nerves  and  Nerve-endings  in  the  Membrana 
Tympani  of  Man,  Amer.  Jour.  Anat.,  vol.  xi,  pp.  101-112. 


CHAPTER  VI 

THE    GENERAL    PHYSIOLOGY    OF    THE    NERVOUS 

SYSTEM 

The  functions  of  the  body  are  generally  effected  by  chemical 
changes  within  its  protoplasm.  These  chemical  changes  in  the 
aggregate  we  term  "metabolism"  and  they  generally  involve  a 
rather  slow  interchange  of  the  chemical  substances  of  food  and 
waste  materials  between  the  cytoplasm  and  the  lymph  which 
surrounds  the  cells  and  between  the  cytoplasm  and  the  proto- 
plasm of  the  nucleus  (karyoplasm) .  The  rate  of  metabolism  is 
dependent  upon  many  factors,  one  of  which  is  the  time  required 
for  the  passage  of  soluble  substances  through  the  cell  membrane 
and  through  the  nuclear  membrane  which  separates  the  cyto- 
plasm from  the  karyoplasm. 

In  the  nerve-cells  both  of  these  sorts  of  chemical  interchange 
are  facilitated  by  the  form  and  internal  structure  of  the  cell. 
As  we  have  already  seen  (p.  41),  the  widely  branching  dendrites 
present  a  large  surface  for  the  absorption  of  food  materials  from 
the  surrounding  lymph  and  the  elimination  of  waste.  The 
specific  nervous  functions  involve  the  consumption  of  living  sub- 
stance, both  in  the  cell  body  and  in  the  nerve-fibers.  This  is 
in  part  an  oxidation  process,  and  this  phase  of  the  activity  can 
be  roughly  measured  by  the  amount  of  carbon  dioxid  eliminated. 
Until  very  recently  it  was  not  possible  to  secure  any  evidence  of 
CO2  production  in  nerve-fibers;  in  view  of  this  and  of  the  further 
fact  that  nerve-fibers  seem  to  be  less  susceptible  to  fatigue  than 
nerve-cells  and  synapses,  many  physiologists  assumed  that 
nervous  conduction  is  not  a  chemical  process,  but  perhaps  some 
sort  of  molecular  vibration.  The  conduction  of  a  nervous  im- 
pulse through  a  living  nerve-fiber  is  accompanied  by  an  electric 
change,  the  so-called  negative  variation,  which  by  some  physi- 
ologists has  been  identified  with  the  nervous  impulse  itself. 
This  and  other  complicated  theories  of  nervous  transmission 

96 


THE  GENERAL  PHYSIOLOGY  OF  THE  NERVOUS  SYSTEM   97 

assume  that  the  process  is  essentially  a  physical  change  (prob- 
ably of  an  electric  nature)  which  involves  no  chemical  altera- 
tions, no  consumption  of  material,  no  metabolism. 

But  by  means  of  recently  devised  apparatus  of  extreme  deli- 
cacy Tashiro  has  shown  very  clearly  and  quantitatively  that 
the  resting  nerve-fiber  eliminates  CO2  and  that  during  functional 
activity  caused  by  stimulation  the  amount  of  CO2  is  increased 
to  about  double  that  of  the  resting  nerve.  The  same  investiga- 
tor subsequently  showed  that  the  amount  of  CO2  given  off  by 
nerve-fibers  is  quite  as  great  per  unit  of  weight  as  that  given  off 
by  the  nerve-cell  bodies  of  the  ganglia.  Tashiro  has  shown, 
moreover,  that  the  rate  of  CO2  production  is  greater  in  that  por- 
tion of  a  nerve-fiber  which  lies  nearer  to  the  source  of  the  stimu- 
lus than  in  a  similar  portion  of  the  same  nerve-fiber  farther  from 
the  receptive  end  and  nearer  to  the  discharging  end.  This  ap- 
plies to  both  sensory  and  motor  fibers.  Child  has  confirmed  this 
by  showing  that  different  parts  of  the  nerve-fiber  show  differ- 
ences in  susceptibility  to  certain  poisons  corresponding  to  the 
differences  in  rate  of  oxidation  of  their  substance.  There  is, 
accordingly,  a  physiological  gradient  in  the  nerve-fiber,  the  physi- 
ological activity  diminishing  in  the  direction  of  the  normal  con- 
duction of  the  nervous  impulse.  The  neuron  is  thus  seen  to 
have  an  intrinsic  physiological  polarity  of  its  own  quite  apart 
from  that  occasioned  by  the  irreversible  character  of  the 
synapse  (see  p.  53). 

It  is,  therefore,  probable  that  the  transmission  of  a  nervous 
impulse  involves  a  wave  of  chemical  change  throughout  the 
length  of  the  nerve-fiber,  though  a  change  of  a  quite  different 
character  from  that  occurring  in  the  cell  body  during  its  func- 
tional activity.  That  the  nervous  conduction  is  not  a  simple 
electric  discharge  through  a  free  conductor,  nor  any  other 
sort  of  simple  ethereal  or  molecular  vibratory  wave  motion,  is 
evident  from  the  fact  that  its  velocity  of  propagation  through 
the  nerve-fiber,  which  is  easily  measured,  is  slower  than  any 
known  wave  movement  of  this  character. 

In  the  unmyelinated  nerves  of  vertebrates  the  rate  of  pro- 
gression of  the  nerve  impulse  varies  from  0.2  to  8  meters  per 
second;  in  the  myelinated  sciatic  nerve  of  the  frog  it  varies 
from  24  to  38  meters  per  second;  and  in  human  myelinated 
7 


98  INTRODUCTION   TO    NEUROLOGY 

nerves  it  may  be  as  rapid  as  125  meters  per  second.  This  rate 
of  conduction  of  the  nervous  impulse  in  peripheral  nerves  varies 
greatly  with  different  animals,  with  different  nerves  in  the  same 
animal,  and  in  the  same  nerve  under  different  physiological  con- 
ditions. 

The  reaction  time  required  for  the  performance  of  various  reflex  acts 
can  be  very  accurately  measured,  and  it  is  found  that  the  time  of  even  the 
simplest  reflex  is  considerably  greater  than  is  required  for  the  transmission 
of  the  nervous  impulse  through  the  conductors  involved.  The  average  rate 
of  conduction  in  human  nerves  is  probably  about  120  meters  per  second,  and 
the  simplest  reaction  times  which  have  been  measured  in  psychological  labor- 
atories vary  between  0.1  and  0.2  second  (from  0.117  to  0.188  for  reactions 
to  touch,  and  from  0.120  to  0.182  for  reactions  to  sound).  The  total  time 
required  for  transmission  of  the  nervous  impulse  through  the  nerve-fibers 
involved  in  these  reactions  need  not  exceed  0.02  second,  whence  it  appears 
that  the  greater  part  of  the  reaction  time  is  otherwise  consumed.  A  part  of 
this  excess  time  is  required  to  overcome  the  inertia  of  the  end-organs 
(receptor  and  effector),  and  the  remainder  is  used  in  the  central  nervous 
system.  This  "central  pause"  is  characteristic  of  all  reflexes  and,  in  fact, 
has  a  profound  significance  in  connection  with  the  evolution  of  the  higher 
associational  functions  of  the  brain.  The  introduction  of  further  complexity 
in  the  reaction,  of  whatever  sort,  usually  lengthens  the  time  of  the  central 
pause,  though  long  training  in  making  a  discriminative  reaction  may  reduce 
this  pause  almost  to  the  time  of  a  simple  reaction. 

Many  attempts  have  been  made  to  determine  the  central  time  of  reac- 
tions of  different  degrees  of  complexity  by  substracting  from  the  total  time 
in  each  case  the  probable  time  required  for  the  peripheral  processes  and  by 
subtracting  the  total  time  required  for  the  simpler  reactions  from  the  total 
time  taken  in  more  complex  discriminative  reactions.  But  further  analysis 
(particularly  more  critical  introspection)  has  shown  that  in  these  human 
reactions  the  problem  is  too  complex  to  be  resolved  by  this  method  (see 
Ladd  and  Woodworth,  1911,  p.  497). 

The  simpler  reflexes  of  lower  vertebrates  can  be  studied  physiologically, 
and  these  give  data  which  are  much  more  readily  analyzed  than  the  more 
complex  human  reactions.  In  the  case  of  the  simplest  reflex  obtainable  in 
the  spinal  cord  of  the  frog,  the  central  pause  was  estimated  by  Wundt  to  be 
only  0.008  second,  i.  e.,  all  of  the  time  required  for  the  reaction  except  this 
interval  was  used  in  the  peripheral  apparatus.  But  in  a  crossed  reflex, 
where  the  reaction  occurs  on  the  opposite  side  of  the  body  from  the  stimu- 
lus, the  increased  complexity  of  the  central  process  consumed  0.004  second 
additional. 

Miss  Buchanan  (1908),  with  more  accurate  methods  of  study,  finds  in  the 
frog  that  the  central  time  varies  between  .014  and  .021  second.  She  also 
measured  the  additional  latent  time  required  for  a  crossed  reflex,  and  found 
it  to  be  of  the  same  order  of  magnitude  as  the  latent  time  of  the  simple 
reflex  (instead  of  half  as  much  as  in  Wundt's  experiments),  that  is,  the 
crossed  reflex  required  about  twice  the  latent  time  in  the  spinal  cord  as  the 
uncrossed  reflex.  It  is  assumed  that  this  central  pause  in  the  uncrossed 
reflex  is  consumed  chiefly  in  the  synapses  between  the  peripheral  sensory 
and  the  peripheral  motor  neurons,  and  that  only  one  such  synapse  is  in- 
volved in  each  simple  reflex  connection  (a  two-neuron  circuit,  see  Fig.  1, 


THE    GENERAL    PHYSIOLOGY    OF    THE    NERVOUS    SYSTEM      99 

p.  25) ;  but  in  the  crossed  reflex  two  such  synapses  are  involved  (a  three- 
neuron  circuit  such  as  the  pathway  from  d.r.S  to  v.r.l'  through  correlation 
neuron  1  in  Fig.  61,  p.  134),  and  the  introduction  of  the  second  synapse 
doubles  the  time.  It  is,  therefore,  a.ssumed  that  it  requires  in  the  frog 
between  .01  and  .02  second  for  the  nervous  impulse  to  pass  the  synapse 
between  two  neurons  in  a  reflex  circuit. 

Turning  now  to  the  activities  of  the  nerve-cell  body,  it  will 
be  recalled  (p.  45)  that  here  the  chromophilic  substance  is  gen- 
erally scattered  throughout  the  cytoplasm  in  the  form  of  the 
"Nissl  bodies."  This  substance  is  very  similar  to  that  of  the 
chromatin  of  the  nucleus,  from  which  it  is  said  to  be  derived 
during  the  development  and  functional  activity  of  the  neuron. 
During  the  resting  state  of  the  cell  it  and  other  reserve  materials 
accumulate  in  the  cytoplasm;  and  now,  when  the  cell  is  stimu- 
lated to  activity,  the  energy  thus  stored  up  may  be  liberated 
almost  instantly  because  the  chemical  substances  necessary  for 
the  reaction  are  widely  diffused  throughout  the  entire  mass  of 
the  cytoplasm. 

The  function  of  neurons,  as  compared  with  that  of  most  other 
cells  of  the  body,  may,  therefore,  be  described  as  of  the  explo- 
sive type.  A  word  of  explanation  will  render  the  analogy  clear. 
In  ordinary  combustion,  oxygen  is  supplied  to  the  surface  of  the 
burning  material,  say  a  blazing  log,  and  the  chemical  process 
of  burning  goes  on  only  as  fast  as  the  superficial  parts  can  be 
oxidized  and  removed.  But  explosive  substances  are  chemic- 
ally so  constituted  that  as  soon  as  combustion  begins  oxygen  is 
liberated  in  the  interior  of  the  material  and  the  process  of  oxi- 
dation takes  place  almost  instantaneously  throughout  the 
entire  mass.  Similarly  in  the  nerve-cell,  the  processes  of  metab- 
olism are  not  dependent  upon  the  slow  interchange  of  substances 
through  the  nuclear  membrane  between  the  cytoplasm  and  the 
nuclear  plasm;  but  the  chromophilic  substance  distributed 
through  the  cj^toplasm  permits  of  much  more  rapid  responses. 
The  organization  of  the  protoplasm  of  the  nerve-cell  is  such 
that  a  very  small  stimulus  may  liberate  a  large  amount  of  energy 
with  explosive  suddenness.  The  energy  thus  liberated  does 
not  all  leave  the  cell,  but  part  of  it  is  directed  into  the  axon, 
which  is  thereby  excited  to  conduct  a  nervous  impulse  to  the 
appropriate  end-organ  or  to  the  next  synapse,  and  thence  to  a 
second  neuron. 


100 


INTRODUCTION  TO   NEUROLOGY 


The  conduction  of  nervous  impulses  within  the  central  nervous 
system  in  some  cases  takes  place  through  well-defined  and  insu- 
lated bundles  of  fibers,  which  are  termed  tracts;  but  in  most 
cases  there  is  more  or  less  complexity  introduced  by  collateral 
avenues  of  discharge  to  other  specific  centers,  as  in  the  complex 
forms  of  reflex  systems  described  in  Chapter  IV,  or  by  a  more 
diffuse  type  of  irradiation  (p.  65).  The  organization  of  the 
central  nervous  system  is  such  that  in  general  the  excitation  of 
any  peripheral  sensory  neuron  may  be  transmitted  to  very  di- 
verse and  remote  parts  of  the  brain,  each  of  which  may  call  forth 
its  own  characteristic  form  of  response. 

The  physiological  effects  of  such  a  dispersal  of  an  incoming  nervous  im- 
pulse within  the  central  nervous  system  may  be  very  different,  depending 


sKin 


Fig.  39. — Diagram  of  an  arrangement  of  neurons  adapted  for  the  dis- 
tribution of  a  single  afferent  nervous  impulse  to  several  different  motor 
organs. 

on  the  connections  of  the  pathways  which  are  taken  by  the  neurons  of  the 
second  order.  If  these  pathways  diverge  so  that  the  stimulus  is  distributed 
among  several  different  effector  systems,  this  would  tend  to  disperse  the 
energy  of  the  afferent  impulse  and  a  relatively  strong  stimulus  is  necessary 
to  call  forth  a  response.  This  is  the  situation  in  case  a  painful  prick  on  the 
skin  of  the  face  calls  forth  reflex  movements  of,  say  (1)  twitching  of  the 
facial  muscles;  (2)  turning  the  head  away,  and  (3)  a  movement  of  the  hand 
to  remove  the  irritant.  Here  the  stimulus  arising  at  a  single  point  in  the 
skin  (Fig.  39)  is  distributed  to  three  widely  separated  motor  centers  {M.l, 


THE  GENERAL  PHYSIOLOGY  OF  THE  NERVOUS  SYSTEM   101 


5Kin 


muscle 


M.3,  M.S).  On  the  other  hand,  in  case  the  stimulus  received  by  the 
neuron  of  the  first  order  is  distributed  to  several  neurons,  all  of  which  dis- 
charge into  the  same  motor  center,  the  stimulus  may  be  reinforced  because 
each  neuron  of  the  second  order  may  discharge  its  own  reserve  energy  in 
such  a  way  as  to  send  out  a  stronger  impulse  than  the  one  received,  so  that 
the  total  discharge  into  the  motor 
center  is  greatly  strengthened  (Fig. 
40) .  Such  an  impulse  may  be  said 
to  accumulate  momentum  as  it  ad- 
vances Uke  an  avalanche  on  a  moun- 
tain slope,  and  hence  this  type  of  re- 
action has  been  termed  by  Ramon 
y  Cajal  "avalanche  conduction." 
In  some  parts  of  the  brain  there  are 
very  special  mechanisms  for  this  sort 
of  cumulative  discharge,  as  in  the 
cortex  of  the  cerebellum  (p.  192)  and 
the  olfactory  bulb  (p.  218). 

The  intensity  of  nervous  dis- 
charge in  all  of  its  forms  is  very 
dependent  upon  the  general  physio- 
logical state  of  the  body,  some  con- 
ditions, such  as  fatigue  and  various 
intoxications,  tending  to  depress  the 
activity,  and  other  conditions  tend- 
ing to  facilitate  it.  The  main- 
tenance of  good  nervous  tone  is, 
therefore,  essential  to  the  highest 
efficiency.      Some  of  these  physio- 


Fig.  40. — Diagram  of  the  mechan- 
ism of  reinforcement  whereby  a 
single  weak  afferent  nervous  im- 
pulse may  be  received  by  several 
neurons  of  the  second  order  which 
discharge  their  greatly  strengthened 
nervous  impulses  into  a  single  final 
common  path. 


logical  agents  may  also  act  locally  on  particular  parts  of  the  nervous  system 
and  thus  determine  the  selection  of  one  instead  of  another  out  of  several 
possible  modes  of  response  in  the  variable  type  of  behavior. 

Fatigue  of  nerve-cells  may  be  brought  about  in  two  ways, 
which  have  been  clearly  distinguished  by  Verworn:  (1)  by 
the  consumption  of  reserve  material  from  which  the  energy  of 
the  cell  is  derived  more  rapidly  than  this  material  can  be  re- 
stored, and  (2)  by  the  accumulation  of  waste-products  more 
rapidly  than  they  can  be  eliminated  from  the  cell.  These  forms 
of  fatigue  have  recently  been  named  by  Dolley  respectively 
"fatigue  of  excitation"  and  "fatigue  of  depression." 

In  his  interesting  discussion  of  neuro-muscular  fatigue,  Stiles 
(1914,  p.  101)  enumerates  several  particular  ways  (in  addition 
to  the  two  general  methods  just  mentioned)  by  which  fatigue 
may  be  brought  about,  among  which  are  the  following:  (1) 
fatigue  of  muscle-fibers,  (2)  fatigue  of  the  junction  of  the  motor 
nerve  with  the  muscle-fiber  at  the  motor  end-plate  (see  Fig. 
5,  p.  40),  (3)  fatigue  of  the  nerve-fibers,  (4)  fatigue  of  the  motor 


102  INTRODUCTION  TO  NEUROLOGY 

nerve-cells,  (5)  fatigue  of  the  synapses  between  the  nerve-cells, 
(6)  fatigue  of  the  sense  organs  and  afferent  apparatus^  (7)  fatigue 
of  the  centers  of  voluntary  control.  The  first,  second,  fourth, 
and  fifth  types  commonly  play  a  part  in  ordinary  fatigue,  the 
third  is  insignificant,  and  the  sixth  and  seventh  may  be  present. 
The  synapses  and  the  motor  end-plates  are  probably  especially 
susceptible  to  fatigue  of  depression  by  toxic  substances,  and  the 
muscle-fibers  and  nerve-cell  bodies  to  fatigue  of  excitation  by 
consumption  of  their  material. 

A  resting  neuron  when  excited  to  activity  at  first  increases  in 
size  by  reason  of  the  stimulus  given  to  general  metabolic  activ- 
ity. The  first  signs  of  fatigue  result  from  the  exhaustion  of  the 
oxygen  supply  of  the  cells;  then  follows  the  consumption  of  the 
reserve  food  materials,  chiefly  those  represented  in  the  chromo- 
philic  substance,  with  consequent  shrinkage  of  the  Nissl  bodies. 
In  extreme  fatigue  the  ultimate  dissolution  and  death  of  the  cell 
may  be  hastened  by  the  accumulation  of  toxic  products  of  cell 
metabolism. 

It  appears  to  be  well  established  by  numerous  experimental  studies  that 
at  the  beginning  of  functional  activity  both  the  nucleus  and  the  cytoplasm 
of  the  resting  neuron  are  enlarged,  and  that  with  the  onset  of  fatigue 
there  is  a  shrinkage,  especially  of  the  nucleus,  with  vacuolation  of  the 
cytoplasm  and  solution  of  the  Nissl  bodies  due  to  the  consumption  of  the 
chromophilic  substance  during  activity.  The  neurofibrils  are  also  said  to 
be  modified  during  functional  activity.  After  excessive  activity  they  be- 
come more  slender  and  apparently  increase  in  number,  while  during  rest  and 
after  hibernation  of  those  animals  which  have  this  habit  the  neurofibrils 
become  thicker  and  less  numerous. 

Cells  whose  chromophilic  substance  has  been  consumed  by  active 
function  may  after  rest  return  to  the  normal  form ;  but  if  the  excitation  be 
carried  beyond  the  stage  of  normal  fatigue,  recovery  of  the  neiu-on  is  im- 
possible and  it  gradually  disintegrates,  resulting  in  the  permanent  enfeeble- 
ment  of  the  nervous  system. 

The  observations  of  Dolley  have  suggested  to  him  that  the  volume  of  the 
nucleus  bears  a  constant  relation  to  the  volume  of  the  cytoplasm  in  all 
resting  nerve-cells  of  the  same  type.  In  varying  functional  states  of  excita- 
tion and  depression  this  mass  relation  is  disturbed  in  accordance  with  the 
formula:  Activity  finally  results  in  a  disturbance  of  the  norinal  nucleus- 
cytoplasmic  relation  in  favor  of  the  cytoplasm  (fatigue  of  excitation),  while 
depression  resulting  from  accumulated  toxins  finally  results  in  a  disturbance 
of  this  relation  in  favor  of  the  nucleus.  In  short,  the  depression  of  the 
neuron  by  any  form  of  intoxication  or  otherwise  gives  the  converse  picture 
of  structural  changes  from  that  presented  by  fatigue  of  excitation. 

Most  of  the  physiological  work  which  has  been  done  upon  fatigue  has  been 
directed  toward  the  isolation  of  special  toxic  substances  such  as  in  Dolley's 
scheme  would  produce  "fatigue  of  depression."     It  has  been  shown  that 


THE  GENERAL  PHYSIOLOGY  OF  THE  NERVOUS  SYSTEM   103 

proloiifiod  muscular  exertion  iiroduces  toxins  (carbon  dioxid,  lactic  acid,  and 
others)  which  are  dissolved  in  the  blood  and  exert  a  profound  de]iressin}2; 
influence  upon  all  of  the  tissues  of  the  body.  If  the  blood  of  a  fatigued 
animal  be  injected  into  or  transfused  with  a  perfectly  fresh  animal  of  the 
same  species,  the  latter  immediately  manifests  all  the  signs  of  fatigue. 

It  is  often  taught  that  a  change  of  work  is  physiologically  equivalent  to 
complete  rest.  It  is  true  that,  so  long  as  one  is  well  within  the  limits  of 
extreme  fatigue,  a  change  of  work  will  prolong  efficiency  far  beyond  that 
which  would  be  possible  in  continuous  activity  of  a  single  nervous  or  mus- 
cular mechanism.  Nevertheless  experiment  shows  that  mental  efficiency 
is  greatly  imi^aired  in  extreme  muscular  fatigue,  and,  conversely,  muscular 
power  is  greatly  weakened  after  long  sustained  mental  work.  Glandular 
secretions  are  also  apparently  often  reduced  in  extreme  fatigue,  thus,  for 
instance,  reducing  the  efficiency  of  the  digestive  organs.  These  effects  are 
doubtless  clue  to  the  accmiiulation  of  toxic  products  in  the  blood,  producing 
a  true  "fatigue  of  depression"  throughout  the  entire  body. 

It  has  been  suggested  that  the  local  feelings  of  muscular  fatigue  are  due 
to  excitations  of  the  organs  of  the  muscular  sense  in  the  muscle  spindles  (p. 
87) ;  but  the  evidence  for  this  does  not  seem  very  convincing. 

The  experiments  of  DoUey  suggest  to  him,  further,  that  the  more  highly 
differentiated  nerve-centers  are  more  susceptible  to  the  structural  altera- 
tions of  fatigue  than  are  those  of  the  lower  reflex  systems.  It  is  a  well- 
known  fact  that  sustained  mental  work  produces  the  subjective  evidences 
of  fatigue  more  promptly  than  does  muscular  work,  and  that  during  severe 
mental  training  one  is  more  apt  to  go  "stale"  than  during  physical  training. 
This  principle  has  been  widely  recognized  in  the  provision  of  short  work- 
ing hours  and  frequent  holidays  for  pupils  and  teachers  in  our  schools;  it 
should  be  still  further  extended,  especially  in  commercial  and  professional 
life.  Its  neglect  is  in  large  measure  responsible  for  the  prevalence  of  neu- 
rasthenia and  other  forms  of  nervous  breakdown. 

The  early  fatigue  of  the  higher  voluntary  centers  is  particularly  evident 
in  young  children,  where  continuous  sustained  attention  is  impossible  except 
for  very  short  periods.  By  training,  these  periods  can  be  greatly  length- 
ened, the  nervous  mechanism  involved  here  probably  being  the  acquisi- 
tion of  a  wider  range  of  associations  related  with  the  subject  which  occupies 
the  focus  of  attention,  so  that  individual  neurons  or  systems  of  neurons 
which  participate  in  the  functional  complex  may  be  temporarily  rested  while 
other  related  systems  are  brought  into  maximmn  activity,  without  thereby 
interrupting  the  continuous  progress  of  the  train  of  thought. 

The  neurological  basis  of  sleep  is  at  present  wholly  unknown, 
though  the  physiological  phenomena  seem  to  be  in  many  respects 
analogous  with  those  of  fatigue.  Of  the  various  theories  which 
have  been  suggested,  the  two  which  have  excited  greatest  interest 
are:  (1)  the  belief  that  some  soluble  toxin  is  produced  during 
waking  hours  which  induces  sleep  by  a  process  similar  to  that  of 
the  "fatigue  of  depression,"  and  (2)  the  doctrine  of  the  retraction 
of  the  neuron,  which  teaches  that  during  sleep  (and  according 
to  some  authors  in  less  measure  during  fatigue  also)  the  dendrites 
of  the  neurons  retract  toward  their  cell  bodies  and  away  from 


104  INTRODUCTION  TO  NEUROLOGY 

contact  with  the  axons  of  other  neurons  with  which  they  are  in 
synaptic  union,  thus  increasing  the  resistance  to  nerve  conduc- 
tion at  the  synapse. 

Many  physiological  experiments  show  that,  though  the  predis- 
position to  sleep  may  be  brought  about  by  the  accumulation  of 
toxins  in  the  blood  or  by  other  general  causes,  the  actual  falling 
asleep  is  accompanied  by  a  fall  in  blood-pressure,  which  may  be 
the  essential  factor  in  sleep.  Fatigue  of  the  vasomotor  center 
has  been  suggested  as  the  real  physiological  cause  of  sleep.  No 
adequate  proof  of  any  of  these  theories  has  been  brought  for- 
ward. 

The  numerous  theories  regarding  the  neurological  processes 
taking  place  in  the  cerebral  cortex  during  the  progress  of  such 
mental  functions  as  attention,  association  of  ideas,  etc., 
are  likewise  as  yet  entirely  unproved.  It  has  been  suggested 
that  during  cerebral  function  the  resistance  of  some  pathways 
may  be  diminished  by  the  ameboid  outgrowth  of  the  dendrites 
so  as  to  effect  more  intimate  synaptic  union  with  the  physiolog- 
ically related  neurons,  while  the  resistance  of  other  paths  may 
be  increased  by  the  retraction  of  dendrites  from  their  synapses. 
Others  believe  that  the  neuroglia  may  participate  in  the  process 
by  thrusting  out  ameboid  processes  between  the  nervous  ter- 
minals in  the  synapses  and  thus  increasing  the  resistance. 
Lugaro  has  suggested  a  different  interpretation,  in  accordance 
with  which  during  sleep  there  is  a  generally  diffused  extension 
of  all  nervous  processes,  thus  providing  for  the  uniform  diffusion 
of  incoming  stimuli,  while  in  the  state  of  attention  all  of  these 
processes  retract  save  those  which  are  directed  in  some  definite 
direction,  thus  narrowing  the  stream  of  nervous  discharge  so  as  to 
intensify  it  and  direct  it  into  the  appropriate  centers.  There  is 
no  direct  evidence  for  any  of  these  theories,  and  the  scientific- 
ally correct  attitude  toward  them  is  frankly  to  admit  that  at 
present  we  do  not  know  what  physiological  processes  are  in- 
volved in  any  of  these  functions. 

Summary. — The  forms  assumed  by  neurons  are  shaped  in 
part  by  their  nutritive  requirements  and  in  part  by  their  func- 
tional connections.  The  metabolism  of  nervous  protoplasm,  as 
measured  by  its  CO2  output,  is  found  to  be  as  active  in  nerve- 
fibers  as  in  the  cell  bodies.     In  a  nerve-fiber  the  metabolic 


THE  GENERAL  PHYSIOLOGY  OF  THE  NERVOUS  SYSTEM   105 

activity  is  found  to  be  greatly  increased  during  the  transmission 
of  a  nervous  impulse ;  and  nervous  conduction  evidently  involves 
a  chemical  change  in  the  conducting  fiber.  The  rate  of  trans- 
mission of  a  nervous  impulse  depends  on  the  structure  and 
physiological  state  of  the  nerve-fiber  involved.  The  metabolic 
activity  of  the  nerve-cells  is  of  a  very  different  sort  from  that  of 
nerve-fibers,  and  may  be  characterized  as  of  the  explosive  tA'pe. 
There  are  at  least  two  factors  involved  in  the  fatigue  of  the 
nervous  system:  (1)  fatigue  of  excitation,  resulting  from  the 
consumption  of  the  materials  of  its  protoplasm,  and  (2)  fatigue 
of  depression,  resulting  from  the  accumulation  of  toxic  products 
of  cellular  activity.  Each  of  these  processes  produces  its  own 
very  special  series  of  morphological  changes  in  the  neurons. 
The  neurological  functions  involved  in  sleep  and  the  higher 
mental  processes  are  as  yet  unknown. 

Literature 

Buchanan,  Florence.  1908.  On  the  Time  Taken  in  Transmission  of 
Reflex  Impulses  in  the  Spinal  Cord  of  the  Frog,  Quart.  Jour.  Exp.  Physiol., 
vol.  i,  pp.  1-66. 

Child,  C.  M.  1914.  Susceptibiht}^  Gradients  in  xAxiimals,  Science,  N.  S., 
vol.  xxxix,  No.  993,  pp.  73-76. 

DoLLEY,  D.  H.  19il.  Studies  on  the  Recuperation  of  Nerve-cells  After 
Functional  Activitj'  from  Youth  to  SeniHty,  Jour.  Med.  Research,  vol.  xxiv, 
pp.  309-343. 

— .  1914.  On  a  Law  of  Species  Identity  of  the  Nucleus-plasma  Norm 
for  Nerve-cell  Bodies  of  Corresponding  Tj^es,  Jour.  Comp.  Neur.,  vol. 
xxiv,  pp.  44.5-501. 

— .  1914.  Fatigue  of  Excitation  and  Fatigue  of  Depression,  Intern. 
Monatsschrift  f.  Anat.  u.  Phj'sioL,  Bd.  31,  pp.  35-62. 

Donaldson,  H.  H.  1899.  The  Growth  of  the  Brain,  New  York,  chapters 
xiv  to  xvii. 

Hodge,  C.  F.  1892.  A  Microscopical  Study  of  Changes  Due  to  Func- 
tional Activity  in  Nerve-cells,  Jour.  ^Morphology,  vol.  vii,  pp.  95-168. 

Ladd,  G.  T.,  and  Woodworth,  R.  S.  1911.  Elements  of  Physiological 
Psychology,  New  York. 

Stiles,  P.  G.  1914.  The  Nervous  System  and  Its  Conservation,  Phila- 
delphia. 

Tashiro,  S.  1913.  Carbon  Dioxide  Production  from  Nerve-fibers  when 
Resting  and  when  Stimulated;  a  Contribution  to  the  Chemical  Basis  of 
Irritability,  Amer.  Jour,  of  Physiol.,  vol.  xxxii,  pp.  107-136. 

Tashiro,  S.,  and  Adams,  H.  S.  1914.  Carbon  Dioxide  Production  from 
the  Nerve-fiber  in  a  Hydrogen  Atmosphere,  Amer.  Jour,  of  Physiol.,  vol. 
xxxiv,  pp.  40.5-413. 

—  — .  1914.  Comparison  of  the  Carbon  Dioxide  Output  of  Nerve- 
fibers  and  GangUa  in  Limulus,  Jour,  of  Biological  Chemistrj',  vol.  xviii, 
pp.  329-334. 


CHAPTER  VII 

THE  GENERAL  ANATOMY  AND  SUBDIVISION  OF  THE 
NERVOUS    SYSTEM 

On  merely,  topographic  grounds  the  nervous  organs  are  divided 
into  the  central  nervous  system,  or  axial  nervous  system,  compris- 
ing the  brain  and  spinal  cord,  and  the  peripheral  nervous  system, 
including  the  craniaLand  spinal  nerves,  their  ganglia  and  periph- 
eral end-organs,  and  the  sympathetic  nervous  system.  The 
nerves  are  simply  conductors,  putting  the  end-organs  into  phys- 
iological connection  with  their  respective  centers.  The  general 
form  of  the  human  central  nervous  system  and  its  connections 
with  the  peripheral  nerves  are  seen  in  Fig.  41.  The  nerves 
connected  with  the  spinal  cord  are  the  spinal  nerves,  those  con- 
nected with  the  brain  are  the  cranial  or  cerebral  nerves,  and 
both  of  these  systems  of  nerves  together  are  called  the  cerebro- 
spinal nerves,  in  contrast  with  the  sympathetic  nerves,  which 
latter  may  or  may  not  be  connected  with  the  central  nervous 
system  (see  p.  225). 

The  central  nervous  system  is  the  great  organ  of  correlation 
and  integration  of  bodily  processes.  Its  primitive  form  in  verte- 
brates is  a  simple  tube,  and  this  is  the  form  shown  in  an  early 
human  embryo  (see  Fig.  46,  p.  116).  The  original  tubular  form 
is  but  little  modified  in  the  trunk  region  of  all  vertebrates,  where 
the  spinal  cord  (medulla  spinalis)  is  formed  by  a  tolerably  uni- 
form thickening  of  the  lateral  walls  of  the  tube  (see  Figs.  41,  58). 
But  in  the  head  region  the  brain  (encephalon)  is  formed  by  the 
very  unequal  thickening  of  different  parts  of  the  walls  of  the  tube 
and  by  various  foldings  brought  about  thereby.  The  general 
arrangement  of  the  human  central  nervous  system  at  successive 
stages  of  development  is  seen  in  Figs.  47-51. 

The  external  form  of  the  brain  has  been  shaped  by  the  space 
requirements  of  the  nerve-cells  and  fibers  which  make  up  its 
substance.  A  group  of  nerve-cells  which  performs  a  single 
function  is  often  spoken  of  as  the  "center"  of  that  function;  but 

106 


I  CERVICAL  NERVB 


•^     I  THORACIC  XERVE 


I  LUMBAR  yERVB 


- -I  SACRAL  IfERVS 

1     ^1  COCCYGEAL  XERVB 
FILVM  TEEMIKALE 

Fig.  41. — The  human  central  nervous  system  from  the  ventral  side, 
illustrating  also  its  connections  with  the  cerebro-spinal  nerv^es  and  with 
the  syinpathetic  nervous  sj-stem,  the  latter  drawn  in  black.  (After  Allen 
Thompson  and  Rauber,  from  Morris'  Anatomy.) 

107 


108  INTRODUCTION  TO  NEUROLOGY 

it  should  be  borne  in  mind  that  this  does  not  imply  that  this 
function  resides  exclusively  in  that  place.  These  functions  are 
all  more  or  less  complex  and  the  "center"  is  usually  the  region 
where  various  nervous  impulses  are  received  and  redistributed; 
it  is,  therefore,  roughly  analogous  with  the  switchboard  of  an 
electric  plant. 

The  nerve-fibers  which  conduct  nervous  impulses  toward  a 
given  center  are  called  afferent,  and  those  which  conduct  away 
from  the  center  are  called  efferent  with  reference  to  that  center. 
Most  of  the  peripheral  nerves  are  mixed,  in  the  sense  that  they 
carry  both  afferent  and  efferent  fibers  with  reference  to  the 
central  nervous  system.  The  efferent  fibers  may  excite  move- 
ment in  muscles  (motor  fibers)  or  secretion  in  glands  (excito- 
glandular  fibers);  other  efferent  fibers  which  check  the  action 
of  the  organ  to  which  they  are  distributed  are  called  inhibitory 
fibers.  The  afferent  fibers  of  the  peripheral  nerves  are  often 
called  sensory  fibers,  though  it  must  be  borne  in  mind  that  their 
excitation  is  not  always  followed  by  sensations  or  other  conscious 
processes. 

The  vertebrate  nervous  system  when  examined  in  the  fresh 
condition  is  found  to  be  made  up  of  white  matter  (substantia 
alba)  and  gray  matter  (substantia  grisea),  the  white  matter 
containing  chiefly  nerve-fibers  with  myelin  sheaths  (see  p.  46) 
and  the  gray  matter  nerve-cell  bodies  and  unmyelinated  fibers. 
The  centers  are,  therefore,  generally  gray  in  color  and  the  inter- 
vening parts  of  the  central  nervous  system  are  white. 

A  group  of  nerve-cells  constituting  a  center  as  above  described  is  often 
called  a  "nucleus,"  a  term  which  has  nothing  to  do  with  the  nuclei  of  the 
individual  cells  (see  p.  39)  of  which  the  center  is  composed.  Some  critical 
writers  use  the  word  "nidulus"  (originally  suggested  by  C.  L.  Herrick)  or 
"nidus"  (Spitzka)  for  such  a  center,  thus  avoiding  the  ambiguity  in  the  use 
of  the  word  nucleus.  The  term  "ganglion"  is  also  sometimes  used  for  nuclei 
or  centers  within  the  brain  (ganglion  habenulse,  ganglion  interpedunculare, 
etc.),  but  this  usage  is  objectionable,  for  the  use  of  the  word  ganglion  in 
vertebrate  neurology  should  be  restricted  to  collections  of  neurons  outside 
the  central  nervous  system,  such  as  the  ganglia  of  the  cranial  and  spinal 
nerves  and  the  sympathetic  ganglia. 

A  nucleus  from  which  nerve-fibers  arise  for  conduction  to  some  remote 
part  of  the  nervous  system  is  called  the  nucleus  of  origin  of  these  fibers; 
conversely,  a  nucleus  into  which  nervous  impulses  are  discharged  by  fibers 
arising  elsewhere  is  the  terminal  nucleus  of  those  fibers.  Any  correlation 
center  is,  therefore,  a  terminal  nucleus  for  its  afferent  fibers  and  a  nucleus 
of  origin  for  its  efferent  fibers. 


ANATOMY    AND    SUBDIVISION    OF    NERVOUS    SYSTEM         109 

The  centers  or  nuclei  within  the  brain  are  of  two  general  sorts : 
(1)  primary  centers  and  (2)  correlation  centers.  The  primary 
centers  are  directly  connected  with  peripheral  nerves,  either  as 
terminal  nuclei  of  afferent  fibers  or  as  nuclei  of  origin  of  efferent 
fibers  (see  pp.  42,  108).  The  elements  out  of  which  most  acts  are 
compounded  are  reflexes  (see  p.  56),  and  in  the  simplest  of  these 
reflexes  a  sensory  nervous  impulse  received  from  the  periphery 
by  a  terminal  nucleus  may  be  passed  on  to  a  nucleus  of  origin  and 
thence  directly  to  the  organ  of  response;  but  in  more  complex 
reflexes  the  incoming  nervous  impulse  is  first  transmitted  from 
the  terminal  nucleus  to  a  correlation  center,  where  it  may  meet 
other  types  of  sensory  impulses  and  then  be  discharged  into  any 
one  of  several  possible  motor  pathways.  For  illustrations  of 
these  types  of  connection  see  Chapter  IV. 

In  general,  ganglia  or  nerve-centers  are  interpolated  in  con- 
duction pathways  only  where  some  complication  of  the  reaction 
is  to  be  provided.  The  conduction  path  is  usually  here  inter- 
rupted by  synapses  and  various  forms  of  correlation  or  coordina- 
tion mechanisms  are  present  (see  p.  35  and  Chapter  IV). 
Many  of  the  sympathetic  ganglia  provide  the  mechanism  for 
local  reflexes  in  which  the  central  nervous  system  does  not  par- 
ticipate (p.  225).  The  spinal  ganglia  (see  Fig.  1,  p.  25)  are 
often  regarded  as  merely  trophic  centers  for  the  maintenance  of 
the  fibers  of  the  peripheral  nerves;  but  they  evidently  have 
functions  of  correlation  in  addition  to  this,  for  numerous  syn- 
apses between  sympathetic  and  cerebro-spinal  neurons  occur 
here  (see  p.  228  and  Fig.  109)  which  play  a  part  in  the  correla- 
tion of  visceral  and  somatic  reactions. 

The  primary  centers  and  the  simpler  correlation  centers  of  the 
brain  can  be  studied  much  more  readily  in  the  brains  of  fishes, 
which  lack  the  cerebral  cortex  whose  enormous  development  in 
the  human  brain  has  obscured  the  relations  and  connections  of 
the  more  primitive  reflex  apparatus.  Figures  42,  43,  and  44  illus- 
trate the  relations  of  the  principal  sense  organs  to  the  brain  in  a 
small  shark,  the  common  marine  dogfish.  Figures  42  and  43 
(on  the  right  side)  illustrate  the  arrangement  of  the  principal 
roots  and  branches  of  the  cranial  nerves.  On  the  left  side  of 
Fig.  43  the  relations  of  the  nose,  the  eye,  and  the  ear  to  the 


no 


INTRODUCTION   TO    NEUROLOGY 


brain  are  indicated;  and  Fig.  44  shows  an  enlarged  side  view 
of  the  brain  and  the  sensory  roots  of  the  cranial  nerves. 


alfs 


Iixtr  can-r-' 


~x     ^iJS-htyrnneZ.VS 


cL.3 


sp.  CO         Lett,  ^''ci^ 


Fig.  42. — Dissection  of  the  brain  and  cranial  nerves  of  the  dogfish, 
Scyllium  catulus.  The  right  eye  has  been  removed.  The  cut  surfaces 
of  the  cartilaginous  skull  and  spinal  column  are  dotted,  cl.l-d.5,  Bran- 
chial (gill)  clefts;  ep.,  epiphysis;  ext.red.,  external  rectus  muscle  of  the 
eyeball;  gl.ph.,  glossopharyngeal  nerve;  hor.can.,  horizontal  semicircular 
canal;  hy.nind.VII,  hyomandibular  branch  of  the  facial  nerve;  inf. obi., 
inferior  oblique  muscle;  int. red.,  internal  rectus  muscle;  lat.vag.,  lateral 
hne  branch  of  the  vagus  nerve;  mnd.V,  mandibular  branch  of  the  trigeminal 
nerve;  mx.V,  maxillary  branch  of  trigeminus;  olf.cps.,  olfactory  capsule; 
olf.s.,  olfactory  sac;  oph.V.VII,  superficial  ophthalmic  branches  of  the 
trigeminal  and  facial  nerves;  path.,  trochlear  nerve  (patheticus) ;  pl.VII, 
palatine  branch  of  facial  nerve;  s.obl.,  superior  oblique  muscle;  sp.co., 
spinal  cord;  spir.,  spiracle;  s.red.,  superior  rectus  muscle;  vag.,  \a,gns  nerve; 
vest.,  vestibule.  (After  Marshall  and  Hurst,  from  Parker  and  Haswell's 
Zoology.) 


In  fishes  there  is  a  system  of  small  sensory  canals  widely  dis- 
tributed under  the  skin.  These  contain  sense  organs  somewhat 
similar  to  those  in  the  semicircular  canals  of  the  internal  ear,  and 


ANATOMY    AND    SUBDIVISION    OF    NERVOUS    SYSTEM         111 

their  functions  are  probably  intermediate  between  ttiose  of  the 
organs  of  touch  in  the  skin  and  those  of  the  internal  ear,  respond- 


Olfactory  bulb 

Olfactory  nerve 

(n.I) 
Somatic  area 


r.  ophthal.  superfic.  V 
r.  ophthal.  superfic.  VII 

n.  terminalis 

r.  ophthal.  profundus  V 

Optic  ner\'e  (n.  II) 


r.  maxillaris  V 
r.  mandib.  V 

Supra-orbital  trunk 

Infra-orbital  trunk 
Ganglion  V 
r.  palatinus  VU. 
Gang,  geniculi  \7I 
Gang,  later.  MI 
r.  pre.spirac.  VII 

Spiracle 

r.  hyomandib.  VII 

n.  IX 
n.  X 

r.  lateralis  X 

r.  branchialis  X 
r.  intestinalis  X 


Fig.  43. — Diagram  of  the  brain  and  sensory  nerves  of  the  smooth  dog- 
fish, Mustehis  canis,  from  above.  Natural  size.  The  Ronian  numerals 
refer  to  the  cranial  nerves.  The  olfactory  part  of  the  lirain  is  dotted,  the 
visual  centers  are  shaded  with  oblique  cross-hatching,  the  acoustico-lateral 
centers  with  horizontal  lines,  the  visceral  sensory  area  with  vertical  lines, 
and  the  general  cutaneous  area  is  left  un.shaded.  (^n  the  right  side  the 
lateral  line  nerves  are  drawn  in  black,  the  other  nerves  are  unshaded. 


112 


INTEODUCTION   TO    NEUROLOGY 


ing  to  water  vibrations  of  slow  frequency  and  probably  assisting 
in  the  orientation  of  the  body  in  space.  These  are  the  lateral 
line  canals.  They  are  innervated  by  special  roots  of  the  VII  and 
X  pairs  of  cranial  nerves  (the  lateralis  roots  of  these  nerves), 
which  are  drawn  in  black  in  Figs.  43  and  44.  The  other  nerves 
are  lightly  shaded  or  white.  The  lateral  line  organs  and  their 
nerves  are  entirely  absent  in  higher  vertebrates  (see  p.  199). 

The  lateral  line  nerves  and  the  acoustic  nerve  (VIII  pair)  in 
fishes  terminate  in  a  common  center  within  the  brain  (the  acous- 
tico-lateral  area),  which  is  shaded  with  horizontal  cross-hatch- 
ing in  Figs.  43  and  44.  The  nerves  of  general  cutaneous  sen- 
sibility also  terminate  in  a  particular  region  which  is  unshaded 


Supra-orbital  trunk 


Optic  lobe 

Epithalamus. 
Thalamus. 


Acoustico-lateral  area 
Gang,  lateralis  VII 


Hypothalamus' 

Ganglion  V 

Infra-orbital  trunk 


auL     hX 

r.  hyomandibularis  VII 

Spiracle 

r.  palatinus  VII 


Ganglion  geniculi  VII 

Fig.  44. — The  same  brain  as  Fig.  43  seen  from  the  side  and  slightly  enlarged. 

and  marked  "general  cutaneous  area."  The  visceral  nerves 
from  the  gills,  stomach,  etc.,  all  enter  a  single  "visceral  area," 
which  is  shaded  with  vertical  lines.  The  eye  is  also  connected 
with  a  special  region  in  the  midbrain,  the  "optic  lobe/'  which  is 
shaded  with  oblique  cross-hatching;  and  the  nose  is  connected 
with  a  part  of  the  forebrain  which  is  stippled. 

We  may,  therefore,  recognize  in  this  fish  a  "nose  brain,"  an 
"eye  brain,"  an  "ear  brain,"  a  "visceral  brain,"  and  a  "skin 
brain,"  each  of  these  peripheral  organs  having  enlarged  primary 
terminal  nuclei  which  make  up  definite  parts  of  the  brain  sub- 
stance. Remembering  that  the  primitive  brain  was  a  simple 
tubular  structure,  we  observe  that  each  one  of  the  chief  sense 
organs  and  each  group  of  similar  sense  organs  sends  sensory 


ANATOMY    AND    SUBDIVISION    OF    NERVOUS    SYSTEM        113 

nerves  inward  to  terminate  in  a  special  part  of  the  wall  of  the 
primitive  neural  tube,  and  that  here  a  thickening  of  the  wall  of 
the  tube  has  taken  place  to  provide  space  for  the  appropriate 
terminal  nucleus.  It  may  be  noticed,  further,  that  all  of  these 
structures  (except  a  part  of  the  olfactory  centers)  lie  in  the 
dorsal  part  of  the  brain.  An  examination  of  the  primary  motor 
centers  would  show  that  they  are  distributed  in  a  somewhat 
similar  fashion  along  the  ventral  part  of  the  brain. 

The  facts  just  recounted  give  a  clear  picture  of  the  pattern  of 
functional  localization  of  the  primary  reflex  centers  in  a  simple 
type  of  brain,  and  they  show  that  all  of  the  more  obvious  parts 
of  this  brain  except  the  cerebellum  are  in  simple  direct  relation 
with  particular  peripheral  organs.  In  other  words,  nearly  the 
whole  of  this  brain  is  directly  concerned  with  simple  reflexes 
and  (aside  from  the  cerebellum)  no  large  centers  for  the  higher 
types  of  adjustments  are  present.  The  primary  reflex  centers 
are  found  to  be  arranged  in  accordance  with  essentially  the  same 
pattern  in  the  human  and  aU  other  higher  brains,  though  in  these 
cases  the  pattern  is  slightly  modified  and  obscured  by  the  pres- 
ence of  greatly  enlarged  correlation  centers,  of  which  the  cerebral 
cortex  is  the  chief.  The  structure  and  significance  of  the  cere- 
bral cortex  form  the  theme  of  the  last  three  chapters  of  this  work. 

The  central  nervous  system  of  the  earfiest  vertebrates  was 
probably  a  simple  longitudinal  tube  of  nervous  tissue  with  which 
the  peripheral  nerves  were  connected  in  a  segmental  fashion  (see 
p.  28).  This  is  the  permanent  form  of  the  spinal  cord  and  its 
nerves  in  all  vertebrates  (see  p.  125  and  Fig.  41).  In  the  brain 
the  enlargement  of  the  primary  reflex  centers  and  of  the  corre- 
lation centers  directly  related  to  tliem  has  changed  the  form  of 
the  tube  and  disturbed  the  primitive  segmental  arrangement  of 
the  cranial  nerves,  as  is  indicated  in  Figs.  43  and  44.  Never- 
theless, this  more  ancient  part  of  the  brain  is  sometimes  called 
the  segmental  apparatus,  to  distinguish  it  from  two  very  large 
coordination  and  correlation  mechanisms  which  are  of  later 
evolutionary  origin,  namely,  the  cerebellar  cortex  and  the 
cerebral  cortex,  which  are  termed  siipraseg menial  structures. 
The  segmental  apparatus  is  often  called  the  hrain  stem.  It 
includes  practically  all  of  the  fish  brain  (Figs.  43  and  44)  except 
the  cerebellum,  for  in  these  aiiimals  there  is  no  cerebral  cortex. 

8 


114 


INTRODUCTION   TO    NEUROLOGY 


If  in  the  human  brain  we  dissect  away  the  cerebral  cortex  and 
the  cerebellar  cortex  and  the  white  matter  immediately  con- 


Nucleus  lentifonnis 
\ 


Capsula  interna 

(pars  lenticulo- 

caudata) 


Capsula  interna  (pars  lenticulo-thalamica) 
I  Nucleus  caudatus 

,  Nucleus  amygdalffi  (cut) 

Commissura  anterior 
r>C  '  ^'X'  Stria  terminalis 

Capsula  interna  (pars 
sublenticularia) 
l''l  .Nucleus  caudatus 


Tractus.__ 
olfactorius 

Tractus  opticus  ^'^ 
Inf  undibulum  -'' 

Hypophy-  f  anterior  lobe '"' 
sis  cerebri  ( posterior  lobe — 

Tuber  cmereum// 
Corpus  mamillare  /  / 
N.  ooulomotorius  / 
Basis  pedunculi'  / 
Pons''  ,' 
■Nervus  trigeminus  (portio  maior)-^^' 
Nervus  trigeminus  (portio  minor).^ 
N.  facialis-' ^^ 
N.  intermedius"^'- 
N.  acusticus^^- 
N.  abducens 
N.  glossopharyngeus^  , 
Nervus  vagus -j  ., 

Pyiamis' 

OUva- 

Fasciculus  circumolivaris  pyramidia" 


"■~"»j^^Thalamus 

Corpus  geniculatum 
laterale 

^'\) -Corpus  pmeale 

xii-- J^~~-Cor.  geniculatum  mediale 
"--CoUiculus  superior 
J Colliculus  mferior 

^>^~~-^^^"  Lemniscus  lateralis 
Nervus  trochlearis 
Brdchium  conjuncti^oim 

>^ 

.^^xssst.^ Brachium 

pontis 

s^-^ Fossa  flocculi 

— Crus  flocculi 
-Nucleus  denta- 
up,       tuscerebelli 

Corpus  ponto-bulbare 


Fasciculus  spinocerebellaris 

__  Nervus  spinalis 


Fig.  45. — ^Left  lateral  aspect  of  a  human  brain  from  which  the  cerebral 
hemisphere  (with  the  exception  of  the  corpus  striatum,  the  olfactory  bulb 
and  tract,  and  a  small  portion  of  the  cortex  adjacent  to  the  latter)  and  the 
cerebellum  (excepting  its  nucleus  dentatus)  have  been  removed.  The 
brain  stem  (segmental  apparatus,  palseencephalon)  includes  everything 
here  shown  with  the  exception  of  the  strip  of  cortex  above  the  tractus 
olfactorius  and  the  nucleus  dentatus.  Within  its  substance,  however,  are 
certain  cortical  dependencies  (absent  in  the  lowest  vertebrates),  which 
have  been  developed  to  facilitate  communication  between  the  brain  stem 
and  the  cerebral  cortex.  The  chief  of  these  are  found  in  the  thalamus, 
basis  pedunculi,  and  pons.  Compare  this  figure  with  the  side  view  of  the 
intact  brain,  Fig.  54.     (Modified  from  Cunningham's  Anatomy.) 


nected  therewith  we  have  the  form  shown  in  Fig.  45. 
the  human  brain  stem. 


This  is 


ANATOMY    AND    SUBDIVISION    OF    NERVOUS    SYSTEM         115 

The  cerebellum  appears  in  the  evolutionary  history  of  the 
vertebrate  brain  much  earlier  than  the  cerebral  cortex;  its 
functions  are  wholly  reflex  and  unconscious  (sec  pp.  158,  186) 
and  are  concerned  chiefly  with  motor  coordination,  equilibra- 
tion, and,  in  general,  the  orientation  of  the  body  and  its  members 
in  space.  Its  activities  are  of  the  invariable,  innate,  structurally 
predetermined  type  (see  pp.  22,  31,  78).  The  cerebral  cortex, 
on  the  other  hand,  is  the  organ  of  the  highest  and  most  plastic 
correlations,  which  are  in  large  measure  individually  acquired. 
It  attains  its  maximum  size  in  the  human  brain. 

In  recognition  of  the  late  phylogenetic  origin  of  the  cerebral 
cortex  Edinger  has  called  the  entire  brain  stem  and  cerebellum 
the  old  brain  (palseencephalon),  and  the  cerebral  cortex  and 
parts  of  the  brain  developed  in  relation  therewith  the  new  brain 
(neencephalon). 

The  terminology  of  the  brain  is  in  great  confusion.  Most  of 
the  more  obvious  parts  were  named  before  their  functions  were 
known,  the  same  part  often  receiving  many  different  names,  and 
sometimes  the  same  name  being  applied  to  very  different  parts. 
To  remedy  this  situation  the  German  Anatomical  Society  in 
1895  pubhshed  an  official  list  of  anatomical  terms  which  is  known 
as  the  Basle  Nomina  Anatomica  (commonly  abbreviated  as 
B.  N.  A.).  Each  of  these  terms  has  a  clearly  defined  significance 
and  they  are  now  very  widely  used,  though  many  anatomists 
continue  to  use  some  older  and  unofficial  names.  The  B.  N.  A. 
terms  or  their  English  equivalents  are  used  in  this  work,  save  in 
a  few  cases  which  are  specifically  mentioned.  The  terminology 
of  the  brain  is  based  upon  the  embryological  researches  of  Pro- 
fessor His,  and  can  best  be  outlined  by  reviewing  the  form  of  the 
human  brain  at  a  few  selected  stages  of  development. 

The  B.  N.  A.  terminology  was  developed  with  exclusive  reference  to  the 
human  body.  The  names  of  many  parts  of  the  bodies  of  other  animals  than 
man  and  of  microscopic  structures  in  general  are  not  included.  The  names 
of  this  Ust  are  all  used  and  defined  in  W.  Krause's  Handbuch  dcr  Anatoniie 
des  Menschen,  Leipzig,  1905,  and  in  most  of  the  recent  American  and 
English  text-books  of  anatomy.  At  the  end  of  Ivrause's  book  is  a  very  com- 
plete List  of  synonyms,  including  most  of  the  anatomical  terms  in  use  and 
their  B.  N.  A.  equivalents. 

Following  the  example  of  many  other  recent  anatomists,  we  shall  in  this 
work  replace  the  B.  N.  A.  term  "anterior"  (on  the  front  or  belly  side)  by  the 
word  "ventral,"  and  the  B.  N.  A.  term  "posterior"  (on  the  back  side)  by 


116 


INTRODUCTION   TO    NEUROLOGY 


the  word  "dorsal."  The  head  end  of  the  body  will  be  referred  to  as  the 
"anterior"  or  "cephalic"  end;  the  other  end  of  the  body  as  the  "posterior" 
or  "caudal"  end.  The  terms  "upper"  or  "higher"  and  "lower"  will  refer 
to  the  relations  in  the  erect  human  body.  In  the  nomenclature  of  the 
meduUa  oblongata  (see  p.  122)  and  of  the  thalamus  (p.  167)  our  usage 
departs  shghtly  from  that  of  the  B.  N.  A.  Regarding  the  naming  of  fiber 
tracts  see  page  128. 

Figure  46  illustrates  the  form  of  the  brain  in  a  very  early 
human  embryo.     Its  tubular  form  is  very  evident,  and  in  the 


/inferior  neuropore 


Pallium  of  telencephalon 

D'lencephahrt 


Corpus  striatum 


/Interior  neuropore 

Mesencephalon 
Isthmus 


Mesencephalon 


Optic  recess 

Future  pontine 
Rhombencephalon      flexure 


Rhombencephalon 


Fig.  46. — An  enlarged  model  of  the  brain  of  a  human  embryo  3.2  mm. 
long  (about  two  weeks  old) .  The  outer  surface  is  shown  at  the  left,  and 
on  the  right  the  inner  surface  after  division  of  the  model  in  the  median 
plane.  The  Anterior  neuropore  marks  a  point  where  the  neural  tube 
is  still  open  to  the  surface  of  the  body.  The  Pallium  is  the  region  from 
which  the  cerebral  cortex  will  develop.  The  Optic  recess  marks  the 
portion  of  the  lateral  wall  of  the  Diencephalon  from  which  the  hollow 
Optic  vesicle  has  evaginated.     (After  His,  from  Prentiss'  Embryology.) 


brain  the  diameter  of  the  tube  is  but  little  greater  than  that 
of  the  spinal  cord.  The  walls  are  thin  and  the  cavity  wide. 
In  a  slightly  older  embryo  the  form  is  shown  in  Fig.  47,  and 
Fig.  48  illustrates  diagrammatically  the  median  section  of  an 
embryo  of  about  the  same  age  as  that  shown  in  Fig.  47,  upon 
which  the  regions  as  defined  by  the  B.  N.  A.  are  indicated.    The 


ANATOMY    AND    SUBDIVISION    OF    NERVOUS    SYSTEM        117 
A 


Mesencephalc 


folium 


Meiencephalon 


Optk 


Cerebellum 


Mvslencephalori 


Fig.  47. — Reconstruction  of  the  brain  of  a  6.9  mm.  human  embryo 
(about  four  weeks  old):  A,  Lateral  view;  B,  in  median  sagittal  section; 
Ceph.flex.,  cephalic  flexure.     (After  His,  from  Prentiss'  Embryology.) 


Hypophysis  (anterior  lobe)  -  -7 

Ventro-lateral  plate 
Dorso-lateral  plate    - 


Fig.  48. — Diagram  of  the  inner  surface  of  the  human  brain,  based  on  a 
specimen  of  about  tlie  same  ago  as  shown  in  Fig.  47.  The  shaded  area  is 
the  ventro-lateral  plate  of  the  neural  tube,  giving  rise  to  the  motor  centers. 
Its  upper  boundary  is  marked  by  a  groove  on  the  ventricular  surface,  the 
sulcus  limitans,  which  separates  the  ventro-lateral  plate  from  a  dorso- 
lateral plate  (unshaded),  which  gives  rise  to  the  sensory  centers  and  chief 
correlation  centers.     (After  His,  from  Morris'  Anatomy.) 


Cerebral  peduncley 

Hypothalamur         '  ^ 
Epltlialamus        \    yr 
Thalamus  \     -  -VA 

Diencephaton      ' 
{Inter-bratn)  \ 


Cerebral  aqueduct 

Mesencephalon 
(Mid-brain) 


RhombencepliaHc 
isthmus 


-  y  Lamina   Corp; 
Rhinencephalon ''  terminalis  strialu: 
{Olfactory-brain) 


Fig.  49. — Vertical  median  section  of  a  model  of  the  brain  of  a  human 
embryo  13.6  mm.  long:  1,  Optic  recess,  marking  the  attachment  of  the 
optic  vesicle;  2,  ridge  formed  by  the  optic  chiasma;  3,  optic  chiasm  a; 
4,  infundibular  recess.  The  limiting  sulcus  is  visible  in  the  model,  though 
not  named,  running  upward  from  the  optic  recess  between  the  thalamus  and 
the  hypothalamus.     (After  His,  from  Sobotta's  Atlas  of  Anatomy.) 


Epithalamus  (Corpus  pineale) 
"■       Metathalamus 
(Corpora  geniculata) 


Corpus  stria  turn. -\i- 


Corpora  quadrigemina 


Pedunculus  cerebri 


Khinenceplialou 
Pars  optica  hypothal 
Chiasma  opti 
Hypophys: 

Pars  Dlamillaris  hypothalami 


Medulla  oblongata 


Fig.  50. — A  vertical  median  section  of  a  model  of  the  brain  of  a  human  fetus 
in  the  third  month.     (After  His,  from  Spalteholz's  Atlas.) 
118 


ANATOMY    AND    SUBDIVISION    OF    NERVOUS    SYSTEM 


119 


Eplthalamua 

(Corpus  pineale) 

Corpora 

quadrigeniina 


Rhinencephalon 

Eeccssus  opticus 

Chiasma  opticum    ./    / 
EecessHS  infundibiili  '     / 
Infundibuluni 

redunculus  cerebri 

T,        ri' in  \  m  ■       I       \i:>^^'^^  Vcntriculus  quartus 

Pous  [^  aroii]  \Mue  en-r     •.,  ,  n     vi       . 

Mviy^.^  ^  I        MeduUa  oblongata 

:ephalon\ 

Fig.  51. — Vertical  median  section  of  the  adult  human  brain.     (From  Spalte- 

holz's  Atlas.) 


SULCUS  CJNGULl 
Iniaryitiat  portion) 


svbparietal  sulcus 

PARIETil-OCCIPI- 

TAL  FISSURE 
CALCaRI.XB 

fissure 


CENTRAL  SULCUS  {ROLAXDD 

I  MASSA   INTERMEDIA 

'  !      SULCUS  CIXG  ULI 

I  (subjrontal  portion) 


SULCUS  CORPORIS 
CALLOSI 


UTPOPnTsis 


itosTsru  OF  coKprs  cm-losph 

\    \      \       AXT^RIOK  P.iSOLF.ICTOKT  steers 

\    \         PAROLPACTOnT  A/tEA  lSIiOC.\'S  jin£s) 

\    •  POSTERIOR  PAROLFACTORY  SCLCts 

^SrS-CALLOSAL  Ci'SUS  tPFPtW'CLE  OF 

CORPUS  CiLLOSl'M) 

IXFUXllIBULCil 


Fig.  52. — Vertical  median  surface  of  the  adult  human  brain, 
from  Morris'  Anatomy.) 


(After  Toldt, 


120 


INTRODUCTION   TO    NEUROLOGY 


The  brain  as  a  whole  is  the  encephalon,  and  its  chief  divisions 
are  indicated  by  prefixes  having  a  topographic  significance  ap- 
plied to  this  word.  In  Fig.  48  the  ventral  part  of  the  neural  tube 
is  shaded  to  indicate  the  region  in  which  the  motor  centers  of  the 
adult  brain  are  found.  The  unshaded  part  of  the  figure  indi- 
cates the  region  devoted  to  the  primary  sensory  centers  and  the 


Optic  chiasma 


Infundibulum  s 
Left  corpus  mamillare 

Substantia  perforata    i    i   "^j  v^, 
posterior  "      ' 

Pedunculus  cerebri 


Olfactory  bulb 


Olfactory  tract 


Optic  nerve 

Hubstantia  perfora- 
ta anterior 


Tuber  cinereum 


Abducens  nevre 


Hypoglossal  nerve 


Trochlear  nerve 

Trigeminal 
nerve 


Facial  nerve 
\coustic  nerve 
Nervus  inter- 
medins 
Glossopharyngeal  nerve 


Medulla  oblongata 
Medulla  spinalis  (cut) 


Vagus  nerve 

Accessory  nerve 
Hypoglossal  nerve 


Fig.  53. — Ventral  view  of  the  adult  human  brain.      Compare  Fig.  41. 
(From  Cunningham's  Anatomy.) 


correlation  centers  related  to  them.  The  sensory  and  motor 
regions  are  separated  in  early  embryologic  stages  by  a  longi- 
tudinal fimiting  sulcus  (the  sulcus  limitans).  Comparison  with 
the  figures  of  later  stages  which  follow  shows  that  the  supra- 
segmental  structures  are  developed  wholly  from  the  sensory 
region.     Figures  49  and  50  illustrate  later  stages  of  develop- 


ANATOMY    AND    SUBDIVISION    OF    NERVOUS    SYSTEM 


121 


ment  and  Fig.  51  the  adult  brain  in  median  section.    Tlic  exter- 
nal form  of  the  adult  brain  is  illustrated  also  in  Figs.  52,  53,  54. 


PBECENTKAL  SULCUS 


CENTRAL  SULCUS  i.ROLANDI') 


BOniZONTAL 
RAMUS  OF  IXTER- 
PARIETAL  SULCUS 


SUPE- 
RIOR EX- 
TREMITY! 

; OF 

PARIETO- 


TERSB 
OCCIPI- 
TAL SUL- 


ORBITAL  PORTION 

INFERIOR    1       TRIANGULAR  PORTION 
FRONTAL    . 

GYRUS  OPERCULAR  PORTION  ir 

OPERCULUM 


Fig.  54. — View  of  the  left  side  of  the  adult  human  brain.  Some  of  the 
principal  sulci  and  gyri  are  named.  The  lateral  cerebral  fissure  (sjdvian 
fissure)  is  not  named;  it  lies  immediately  above  the  gyrus  temporalis  supe- 
rior.    (After  Toldt,  from  Morris'  Anatomy.) 

The  following  table  summarizes  the  relations  of  the  subdivis- 
ions of  the  brain  (the  ventricles  of  some  of  them  being  added  in 
parentheses),  to  which  a  few  comments  are  here  added: 

Rhombencephalon,  rhombic  brain  (fourth  ventricle). 
Myelencephalon,  medulla  oblongata. 
Metencephalon. 
Cerebellum. 
Pons. 
Isthmus  rhombencephali. 
Cerebrum. 

Mesencephalon,  midbrain  or  corpora  quadrigemina  and  cerebral  pedimcles 

(aqueduct  of  Sylvius). 
Prosencephalon,  forebrain. 

Diencephalon,  betweenbrain  (third  ventricle). 
Hypothalamus. 
Thalamus. 
Mctathalamus. 
Epithalamus. 
Telencephalon,  endbrain. 
Pars  optica  hypothalami. 
Hemisphseria,  cerebral  hemispheres  (lateral  ventricles). 


122  INTRODUCTION  TO  NEUROLOGY 

The  isthmus  is  a  sharp  constriction  which  separates  the  brain 
into  two  major  divisions,  the  rhombencephalon  behind  and  the 
cerebrum  in  front.  In  the  B.  N.  A.  table  the  isthmus  is  regarded 
as  a  transverse  segment  or  ring;  it  might  better  be  regarded 
simply  as  a  plane  of  separation  between  the  rhombencephalon 
and  cerebrum.  In  the  table  the  medulla  oblongata  is  regarded 
as  synonymous  with  myelencephalon,  that  is,  the  region  between 
the  pons  and  the  spinal  cord.  The  older  usage,  which  is  still 
widely  current,  regards  the  medulla  oblongata  as  including 
everything  between  the  isthmus  and  the  spinal  cord  except  the 
cerebellum  dorsally  and  the  fibers  and  nuclei  of  the  pons  and  mid- 
dle peduncle  of  the  cerebellum  ventrally.  This  is  the  old  or  seg- 
mental part  of  the  rhombencephalon,  and  the  cerebellum  and 
pons  fibers  related  to  it  are  added  to  this  primitive  medulla 
oblongata.  The  older  usage  is  preferable  to  the  B.  N.  A.  division 
and  will  be  adopted  here,  for  the  medulla  oblongata  as  here 
defined  is  a  structural  and  functional  unit,  whose  form  is  not 
modified  in  those  animals  which  almost  totally  lack  the  cere- 
bellum and  its  middle  peduncle.  The  midbrain  (mesencephalon) 
is  the  least  modified  part  of  the  neural  tube  in  the  adult  brain. 
The  betweenbrain  (diencephalon)  has  three  principal  divisions : 
(i)  below  is  the  hypothalamus;  (2)  above  is  the  epithalamus; 
(3)  between  these  is  the  thalamus  which  includes  the  thalamus 
and  metathalamus  of  the  table  (see  p.  167).  The  hypothalamus 
and  epithalamus  are  highly  developed  in  the  lowest  vertebrates 
and  are  related  to  the  olfactory  apparatus;  in  these  brains  the 
thalamus  proper  is  very  small,  this  part  increasing  in  size  in  the 
higher  animals  parallel  with  the  evolution  of  the  cerebral  cortex. 
The  thalamus  proper  is  really  a  sort  of  vestibule  to  the  cere- 
bral cortex ;  all  nervous  impulses  which  reach  the  cortex,  except 
those  from  the  olfactory  organs,  enter  it  through  the  thalamus. 
The  endbrain  (telencephalon)  includes  the  cerebral  hemispheres 
and  a  very  small  part  of  the  primitive  unmodified  neural  tube 
to  which  the  hemispheres  are  attached,  this  being  the  pars 
optica  hypothalami  of  the  table  or,  better,  the  telencephalon 
medium. 

If  now  we  compare  this  subdivision  of  the  human  brain  with 
our  rough  functional  analysis  of  the  fish  brain  (p.  112),  we  notice 
that  the  "ear  brain"  (acoustico-lateral  area),  "skin  brain"  or 


ANATOMY    AND    SUBDIVISION    OF    NERVOUS    SYSTEM        123 

"face  brain"  (general  cutaneous  area),  and  "visceral  brain"  (vis- 
ceral area)  are  all  contained  in  the  rhombencephalon,  whose  seg- 
mental or  stem  portion  is  made  up  of  these  centers  and  the 
corresponding  motor  centers.  The  same  relations  hold  in  the 
human  brain,  and  in  both  cases  the  cerebellum  (and  in  man  the 
pons  in  the  narrower  sense  in  which  I  use  that  term)  is  added  as 
a  suprasegmental  part.  In  both  cases  the  "eye  brain"  includes 
the  retina  of  the  eye,  the  optic  nerve,  and  a  part  of  the  roof  of 
the  midbrain.  In  the  fish  a  very  small  part  of  the  thalamus 
(not  indicated  on  Figs.  43  and  44)  also  receives  fibers  from  the 
optic  nerve.  In  man  this  optic  part  of  the  thalamus  is  greatly 
enlarged,  forming  so  large  a  part  of  that  structure  in  fact  that 
the  thalamus  as  a  whole  is  often  called  the  optic  thalamus.  It 
should  be  remembered,  however,  that  even  in  man  the  optic 
centers  comprise  only  a  part  of  the  thalamus.  The  "nose  brain" 
of  the  fish  comprises  most  of  the  cerebral  hemispheres  (all  except 
the  small  "somatic  area"  of  Fig.  44),  and  all  of  the  epithalamus 
and  hypothalamus.  In  man  these  parts  remain  essentialh"  un- 
changed, but  the  "somatic  area"  of  the  hemisphere  has  greatty 
enlarged  to  form  the  large  corpus  striatum  and  the  enormous 
cerebral  cortex,  the  latter  forming  the  suprasegmental  apparatus 
of  the  telencephalon,  and  greatl}^  modifjnng  the  form  relations 
of  all  adjacent  parts. 

The  details  of  the  development  of  the  brain  lie  outside  the 
scope  of  this  work,  as  also  do  the  anthropological  questions  grow- 
ing out  of  the  statistical  studj^  of  brain  weights^  and  measure- 
ments. These  and  manj'  other  topics  of  fundamental  impor- 
tance are  presented  in  a  very  interesting  waj'  in  Donaldson's 
book  on  The  Growth  of  the  Brain. 

SuTiunary. — In  all  vertebrates  the  central  nervous  system  is 
fundamentally  a  hollow  dorsal  tube  in  which  the  primary  seg- 
mentation is  sul^ordinated  to  the  development  of  important 
longitudinal  correlation  tracts  and  centers.  This  tube  is  en- 
larged at  the  front  end  to  form  the  brain.  The  vertebrate  brain 
may  be  divided  on  physiological  grounds  into  great  divisions, 

1  The  weight  of  the  brain  is  exceedingly  variable,  even  in  a  homogeneous 
population.  The  average  weight  of  the  normal  adult  European  male  brain 
is  commonly  stated  to  be  1360  grams  (4S  oz.),  and  that  of  the  female  1250 
grams  (44  oz.)- 


124  INTRODUCTION  TO  NEUROLOGT 

first  the  brain  stem,  or  primary  segmental  apparatus;  and  second 
the  cerebellum  and  cerebral  cortex,  or  suprasegmental  apparatus. 
The  brain  stem  and  cerebellum  are  devoted  chiefly  to  reflex  and 
instinctive  activities  and  constitute  the  "old  brain"  of  Edinger. 
The  cerebral  cortex  is  devoted  to  the  higher  associations  and 
individually  acquired  activities  and  is  called  the  ''new  brain" 
by  Edinger.  No  nervous  impulses  can  enter  the  cortex  without 
first  passing  through  the  reflex  centers  of  the  brain  stem. 

In  flshes  the  form  of  the  brain  is  shaped  almost  wholly  by  the 
development  of  the  reflex  centers,  and  here  these  mechanisms 
can  best  be  studied,  each  of  the  more  obvious  parts  of  the  brain 
being  dominated  by  a  single  system  of  sensori-motor  reflex  cir- 
cuits. The  same  pattern  is  preserved  in  the  human  brain,  but 
much  distorted  by  the  addition  of  the  centers  of  higher  correla- 
tion. 

The  terminology  of  the  brain  now  in  most  common  use  is 
based  on  its  embryological  development,  which  is  briefly  re- 
viewed. 

Literature 

Barker,  L.  F.  1907.  Anatomical  Terminology,  Philadelphia. 

Donaldson,  H.  H.  1899.  The  Growth  of  the  Brain,  a  Studj'  of  the  Ner- 
vous System  in  Relation  to  Education,  New  York. 

Edinger,  L.  1908.  The  Relations  of  Comparative  Anatomy  to  Com- 
parative Psychology,  Jour.  Comp.  Neur.,  vol.  xviii,  pp.  437-457. 

Herrick,  C.  Judson.  1910.  The  Morphology  of  the  Forebrain  in 
Amphibia  and  Reptiha,  Jour.  Comp.  Neur.,  vol.  xx,  pp.  413-547. 

His,  W.  1895.  Die  anatomische  Nomenclatur:  Nomina  Anatomica, 
Archiv  f.  Anat.  und  Physiol.,  Anat.  Abt.,  Supplement-Band. 

Johnston,  J.  B.  1906.  The  Nervous  System  of  Vertebrates,  Philadel- 
phia. 

— .  1909.  The  Central  Nervous  System  of  Vertebrates,  Ergebnisse  und 
Fortschritte  der  Zoologie,  Bd.  2  Heft  2,  pp.  1-170. 

— .  1909.  The  Morphology  of  the  Forebrain  Vesicle  in  Vertebrates,  Jour. 
Comp.  Neur.,  vol.  xix,  pp.  457-539;  also  important  papers  on  the  same  sub- 
ject in  later  volumes  of  The  Journal  of  Comparative  Neurology. 

Keibel,  F.,  and  Mall,  F.  P.  1912.  Manual  of  Human  Embryology, 
Philadelphia,  vol.  ii,  pp.  1-156. 

Krause,  W.  1905.  Handbuch  der  Anatomic  des  Menschen,  mit  einem 
Synonymenregister,  auf  Grundlage  der  neuen  Baseler  anatomischen  Nomen- 
clatur, Leipzig. 

Retzius,  G.  1896.  Das  Menschenhirn,  2  vols.,  Stockholm. 

Sherrington,  C.  S.  1906.  The  Integrative  Action  of  the  Nervous  Sys- 
tem, New  York. 


CHAPTER  VIII 

THE    SPINAL    CORD    AND    ITS    NERVES 

The  spinal  cord  (medulla  spinalis)  is  the  least  modified  part 
of  the  embryonic  neural  tube,  and  the  spinal  nerves  constitute 
the  only  part  of  the  nervous  system  in  which  the  primitive  seg- 


Posterior  divisi 


Anterior  cutaneous  n. 


Fig.  55. — Diagram  of  a  typical  spinal  nerve  in  the  thoracic  region. 
The  spinal  column  and  the  muscles  are  shown  in  gray,  the  nerves  and  their 
gangha  in  black.     (Modified  from  Gray's  Anatomy.) 


mental  pattern  is  clearly  preserved  in  the  adult  body  (see  p. 
113)  The  spinal  nerves  are  connected  with  the  spinal  cord  in 
serial  order,  a  pair  of  nerves  for  each  vertebra  of  the  spinal 
column  (see  Fig.  41,  p.  107). 

125 


126 


INTRODUCTION   TO    NEUROLOGY 


Each  spinal  nerve  distributes  efferent  (motor)  fibers  to  the 
muscles  and  afferent  (sensory)  fibers  to  the  skin  and  deep  tissues 
of  its  appropriate  segment  of  the  body,  and  through  its  connec- 
tions with  the  sympathetic  nervous  system  it  may  effect  various 
visceral  connections  (Figs.  55  and  56).  The  efferent  fibers 
leave  the  cord  through  the  ventral  roots  of  the  spinal  nerves, 
these  fibers  arising  from  cells  within  the  gray  matter  of  the  cord, 
and  the  afferent  fibers  enter  through  the  dorsal  roots,  these 


DoT^  column \ — | — f 


Dorsal  root 


Lateral  column 


Ventral  column- 


Ventral  root 


Visceral  muscle- 


Mucous  membrane 


li irM>a.Ul«^ 


Ramus  conamunioans 
Sympathetic  ganglion 
Postganglionic  fiber 


Fig.  56. — Diagram  illustrating  the  composition  of  a  typical  spinal  nerve 
in  the  thoracic  region.  The  somatic  sensory  system  is  indicated  by  broken 
lines,  the  visceral  sensory  by  dotted  hnes,  the  somatic  efferent  by  heavy 
continuous  lines,  the  visceral  efferent  by  Ughter  continuous  hnes.  (Compare 
Figs.  1  and  55.) 


fibers  arising  from  cell  bodies  of  the  spinal  ganglia  (see  Fig.  1, 
p.  25,  and  Figs.  55,  56).  The  fibers  of  the  spinal  nerves  are  classi- 
fied in  accordance  with  the  same  physiological  criteria  as  their 
end-organs  (see  pp.  79-94,  and  compare  the  cranial  nerves,  pp. 
143-150)  into  somatic  afferent  (or  sensory),  visceral  afferent 
(or  sensory),  somatic  efferent  (or  motor),  and  visceral  efferent 
(or  motor)  systems  (Fig.  56). 

In  the  spinal  cord  the  originally  wide  cavity  of  the  embryonic 
neural  tube  (see  p.  116)  is  reduced  to  a  slender  central  canal  and 


THE    SPINAL    CORD    AND    ITS    NERVES  127 

the  walls  of  the  tii])e  are  thickened.  The  nerve-cells  retain  their 
primary  position  bordering-  the  central  canal,  thus  forming  a 
mass  of  central  gray  matter  which  is  roughh^  H -shaped  in  cross- 
section.  This  gray  matter  on  each  side  is  accumulated  in  the 
form  of  two  massive  longitudinal  ridges,  a  dorsal  column 
(cohmina  dorsalis,  or  posterior  horn),  whose  neurons  receive 
terminals  of  the  sensory  fibers  of  the  dorsal  roots,  and  a  ventral 
column  (columna  ventralis,  or  anterior  horn)  whose  neurons  give 
rise  to  the  fibers  of  the  ventral  roots. 

The  white  matter  of  the  spiiial  cord  is  superficial  to  the  gray 
and  is  made  up  of  sensor^''  and  motor  root  fibers  of  spinal  nerves, 
ascending  and  descending  correlation  fibers  putting  different 
parts  of  the  cord  into  functional  comiection,  and  longer  ascend- 
ing and  descending  tracts  by  which  the  spinal  nerve-centers 
are  connected  with  the  higher  association  centers  of  the  brain. 
In  general,  the  shorter  fibers  lie  near  to  the  central  gray  and  the 
lonTer  tracts  more  superficially. 

The  white  matter  which  borders  the  gray  in  the  spinal  cord 
is  more  or  less  mingled  with  nerve-cells  and  fine  unmyelinated 
endings,  and  thus  shows  under  low  powers  of  the  microscope  a 
reticulated  appearance.  This  is  the  reticular  formation  (pro- 
cessus reticularis)  of  the  cord  (see  pp.  65,  158,  and  Fig.  58). 
Immediately  surrounding  the  reticular  formation  and  partty 
embedded  within  it  are  myelinated  fibers  belonging  to  neurons 
intercalated  between  the  sensory  and  the  motor  roots,  which 
run  for  relatively  short  distances  in  an  ascending  or  descending 
direction  for  the  purpose  of  putting  all  levels  of  the  cord  into 
functional  connection  in  the  performance  of  the  more  complex 
spinal  reflexes.  These  fibers  form  the  deepest  layer  of  the 
white  matter  and  are  termed  the  fasciculi  proprii  (dorsalis, 
lateralis,  and  ventralis,  see  Fig.  59).  These  fascicles  are  also 
called  ground  bundles  and  fundamental  columns. 

In  the  narrow  space  between  the  ventral  fissure  and  the  cen- 
tral canal  (see  Fig.  58)  there  is  a  bundle  of  nerve-fibers  which 
cross  from  one  side  of  the  spinal  cord  to  the  other.  This  is  the 
ventral  commissure.  A  similar  but  smaller  dorsal  commissure 
crosses  immediateh^  above  the  central  canal. 

There  is  considerable  confusion  in  tlie  terminology  in  use  in  the  further 
analysis  of  the  spinal  white  matter,  and  the  usage  which  follows  differs 


128 


INTEODUCTION   TO    NEUROLOGY 


in  some  respects  from  most  of  the  classical  descriptions,  no  two  of  which 
agree  among  themselves.  We  shaU  limit  the  application  of  the  term 
funiculus  to  the  three  major  divisions  of  the  white  matter  of  each  half  of  the 
spinal  cord,  viz.,  the  dorsal  funiculus  bounded  by  the  dorsal  fissure  and  the 
dorsal  root,  the  lateral  funiculus  lying  between  the  dorsal  and  ventral 
roots,  and  the  ventral  funiculus  between  the  ventral  root  and  the  ventral 
fissure  (Fig.  57). 

Each  funiculus  may  be  divided  in  a  purely  topographic  sense  into 
fasciculi,  or  collections  of  nerve-fibers  which  occupy  the  same  general  region 
in  the  cross-section  of  the  cord,  such  as  the  fasciculus  gracilis  of  Goll  and  the 
fasciculus  cuneatus  of  Burdach  (which  together  make  up  the  greater  part 
of  the  funiculus  dorsalis,  see  Figs.  57  and  59),  and  the  superficial  ventro- 
lateral fasciculus  of  Gowers  (including  among  other  tracts  the  spino- 
tectal tract  and  the  ventral  spino-cerebellar  tract  of  Fig.  59) .  These  fasciculi 
are  usually  mixed  bundles  containing  tracts  of  diverse  functional  types. 


Dorsal  root 

Dorsal  funiculus 

Dorsal  column 

Lateral  funiculus 

Lateral  column 

Ventral  column 

Ventral  funiculus 

Ventral  root 

Fig.  57. — Diagram  of  a  cross-section  through  one-half  of  the  spinal 
cord  to  illustrate  the  arrangement  of  the  funiculi  of  white  matter  and  the 
columns  of  gray  matter. 

The  true  physiological  units  of  the  spinal  white  matter  are  the  tracts,  i.  e., 
collections  of  nerve-fibers  of  similar  functional  type  and  connections. 
These  tracts  by  some  neurologists  are  termed  fascicuh;  and,  like  the  other 
tracts  of  the  central  nervous  system,  they  are,  in  general,  named  in  accord- 
ance with  the  terminal  relations  of  their  fibers,  the  name  of  the  location  of 
their  cells  of  origin  preceding  that  of  their  place  of  discharge  in  a  hyphenated 
compound  word.  Thus,  the  tractus  cortico-spinalis  arises  from  cells  of  the 
cerebral  cortex  (p.  140),  and  terminates  in  the  spinal  cord,  and  the  tractus 
spino-cerebellaris  arises  in  the  spinal  cord  and  terminates  in  the  cerebellum 
(p.  130) .  But,  as  already  stated,  there  is  no  uniformity  in  the  nomenclature 
of  these  tracts  and  no  two  authorities  agree  exactly  in  the  terminology 
adopted.  Moreover,  few  of  the  tracts  have  clearly  defined  anatomical  limits, 
in  most  cases  the  fibers  of  different  systems  being  more  or  less  mingled. 

The  appearance  of  a  cross-section  through  the  spinal  cord  in 
the  lower  cervical  (neck)  region,  after  staining  so  as  to  reveal  the 
arrangement  of  both  the  nerve-cells  and  the  nerve-fibers,  is  seen 


THE    SPINAL    CORD    AND    ITS    NERVES 


129 


in  Fig.  58.      Figure    59    illustrates   diagrammatically   the  ar- 
rangement of  the  chief  fiber  tracts  in  the  same  region. 

The  spinal  cord  has  two  main  groups  of  functions,  first,  as  a 
system  of  reflex  centers  for  all  of  the  activities  of  the  trunk  and 
limbs;  second,  as  a  path  of  conduction  between  these  centers 
and  the  higher  correlation  centers  of  the  brain.  The  former 
group  is  the  more  primitive,  and  there  is  evidence  that  in  the 

Dorsal  median  septum 
Spptum 
Dorsal  lateral  groo\e 

Dorsal  nen-e  root 

Substantia  gelatinos.i 

Root-fibers  enterin] 
matter 
Processus  reticular! 

Central  canal 


Nucleus  from  which 
motor  fiber?  for 
muscles  of  upper 
limb  arise 

Ventral  white  commis- 
sure 


Ventral  nerve  root 

Ventral  median  fissure 


Fig.  58.- — Cross-section  through  the  human  spinal  cord  at  the  level  of 
the  fifth  cervical  nerve,  stained  bj'  the  method  of  Weigert-Pal,  which  colors 
the  white  matter  dark  and  leaves  the  gray  matter  uucolored.  (From 
Cunningham's  Anatomy.) 

course  of  vertebrate  evolution  the  higher  centers,  especially  the 
cerebral  hemispheres,  exert  an  increasingly  greater  functional 
control  over  these  reflex  centers  (see  p.  280).  The  long  conduc- 
tion paths  between  the  spinal  cord  and  the  cerebral  hemispheres 
are,  accordingly,  much  larger  in  man  than  in  lower  vertebrates. 
It  is  impossible  in  the  space  at  our  disposal  to  summarize  even 
the  most  important  of  the  internal  connections  of  the  spinal 
nerves;  we  can  only  select  a  few  tj-pical  illustrative  examples. 
9 


130 


INTRODUCTION   TO   NEUROLOGY 


Fasc.  gracilis' 

Fasc.  cuneatus 

Fasc.  septo-marg. 

Fasc.  inter-fascic. 

Tr.  cortico-spin.  lat. 

Tr.  mbro-spin. 

Nuc.  dorso-lat. 

Nuc.  ventro-med 

Nuc.  ventro-lat., 

Tr.  cortico-spin.  ven . 

Tr.  olivo-spinalis 

Tr.  teoto-spinalis 

Tr.  vestibulo-spin. 

Radix  ventralis 


Radix  dorsalis 
Fasc.  dorso-lat. 
■Tr.  spino-oereb.  dor. 
■  Columna  dorsalis 
■Fasc.  proprius  dors. 
Fasc.  proprius  lat. 
Tr.  spino-cereb.  ven. 
-Tr.  spino-thalam.  lat. 
■Columna  ventralis 
-Tr.  spino-tectalis 
-Tr.  spino-thalam.  ven. 
-Tr.  spino-olivaris 
Fasc.  proprius  ven. 
Fasc.  sulco-marg. 


Fig.  59. — Diagram  of  a  cross-section  through  the  human  spinal  cord  at 
the  level  of  the  fifth  cervical  nerve,  to  illustrate  arrangement  of  the  fiber 
tracts  in  the  white  matter  and  of  the  nerve-cells  in  the  gray  matter  of  the 
ventral  column.  On  the  right  side  the  area  occupied  by  the  dorsal  gray 
column  (posterior  horn)  is  stippled;  on  the  left  side  some  of  the  groups  of 
cells  of  the  ventral  gray  column  (anterior  horn)  are  indicated.  In  the  white 
matter  the  outlines  of  some  of  the  more  important  tracts  are  schematically 
indicated,  ascending  fibers  on  the  right  side  and  descending  fibers  on  the 
left.  The  same  area  of  white  matter  is  in  some  cases  shaded  on  both  sides 
of  the  figure.  This  indicates  that  ascending  and  descending  fibers  are 
mingled  in  these  regions.  A  list  of  the  tracts  here  illustrated  follows.  The 
names  here  employed  in  some  cases  differ  from  those  of  the  official  German 
Anatomical  Society  list  (see  p.  115),  the  B.  N.  A.  terms  here  being  itahcized. 

Ascending  Tracts 

Fasciculus  gracilis  (colmnn  of  Goll)  and  fasciculus  cuneatus  (column  of 
Burdach.)  These  are  mixed  bundles  which  in  the  aggregate  make  up  the 
greater  part  of  the  dorsal  funiculus  (old  term,  posterior  columns) .  They  are 
made  up  chiefly  of  the  ascending  branches  of  dorsal  root  fibers  (see  Fig.  61), 
those  in  the  gracilis  from  the  sacral,  lumbar,  and  lower  thoracic  nerves  {S, 
L,  T5-12),  and  those  in  the  cuneatus  from  the  upper  thoracic  and  cervical 
nerves  {Tl-4,  C),  as  indicated  in  the  figure.  These  fascicuh  terminate 
respectively  in  the  nuclei  of  the  fasciculus  gracihs  (clava)  and  cuneatus 
(tuberculum  cuneatum)  at  the  lower  end  of  the  medulla  oblongata  (cf.  Fig. 
83),  and  conduct  chiefly  impulses  of  the  proprioceptive  reflexes  and  those 
concerned  with  sensations  of  posture,  spatial  discrimination,  and  the  co- 
ordination of  movements  of  precision  (see  pp.  137,  175). 

Fasciculus  dorso-lateralis  (tract  of  Lissauer,  Lissauer's  zone),  made  up 
chiefly  of  unmyelinated  fibers  from  the  dorsal  roots,  together  with  myelin- 
ated correlation  fibers  of  the  fasciculus  proprius  system. 

Tractus  spino-cerebellaris  dorsalis  (fasciculus  cerebello-spinalis,  direct 
cerebellar  tract,  Flechsig's  tract) .  These  fibers  arise  from  the  neurons  of  the 
nucleus  dorsalis  (Clarke's  column  of  gray  matter  between  the  dorsal  and 
ventral  gray  columns  in  the  thoracic  region,  also  called  Stilling's  nucleus) 
of  the  same  side  and  enter  the  cerebellum  by  way  of  its  inferior  peduncle 
(corpus  restiforme). 

Tractus  spino-cerebellaris  ventralis  (part  of  Gowers'  tract,  or  the  fascicu- 
lus antero-lateralis  swperficialis  of  the  B.N.  A.).  These  fibers  also  arise  from 
the  nucleus  dorsalis  of  the  same  side  (A.  N.  Bruce)  in  the  lower  levels  of  the 


THE    SPINAL    CORD    AND    ITS    NERVES  131 

spinal  cord  and  enter  the  cerebellum  by  way  of  its  superior  peduncle  {bra- 
chiurn  conjundivum) . 

The  spinal  lemniscus.  Under  this  name  are  included  several  tracts  to 
the  midbrain  and  thalamus.  These  fibers  arise  from  neurons  of  the  dorsal 
gray  column,  cross  in  the  ventral  commissure,  and  ascend  in  the  lateral  and 
ventral  funicuh  of  the  opposite  side,  partly  superficially  mingled  with  those 
of  the  ventral  spino-cerebellar  tract  and  partly  deej^er  in  the  fasciculus 
proprius.  This  system  of  fibers  includes  a  tractus  spino-tectalis  to  the  roof 
(tectum)  of  the  midbrain  and  a  tractus  spino-thalamicus  to  the  ventral  and 
lateral  nuclei  of  the  thalamus.  The  deeper  fibers  of  the  latter  tract  are 
arranged  in  two  groups,  the  tractus  spino-thalamicus  laterahs  for  sensory 
impulses  of  temperature  and  pain,  and  the  tj;^actus  spino-thalamicus  ven- 
trahs  for  sensory  impulses  of  touch  and  pressure  (see  p.  138,  173). 

Tractus  spino-olivaris,  fibers  arising  from  the  entire  length  of  the  spinal 
cord  and  terminating  in  the  inferior  ohve  (Goldstein). 

Descending  Tracts 

Tractus  cortico-spinalis  (fasciculus  cercbro-spinalis,  pjrramidal  tract). 
This  system  of  fibers  conducts  voluntary  motor  impulses  from  the  precentral 
gyrus  of  the  cerebral  cortex  to  the  motor  centers  of  the  spinal  cord.  It  di- 
vides at  the  upper  end  of  the  spinal  cord  into  two  tracts,  the  larger  division 
immediately  crossing  through  the  decussation  of  the  pyramids  to  the  oppo- 
site side  of  the  spinal  cord,  where  it  becomes  the  tractus  cortico-spinahs 
laterahs  (fasciculus  cerebro-spinalis  lateralis,  lateral  or  crossed  pyramidal 
tract).  A  smaller  number  of  these  fibers  pass  downward  into  the  spinal 
cord  from  the  medulla  oblongata  without  decussation  to  form  the  tractus 
cortico-spinaUs  ventralis  (fascieulu^  cerebro-spinalis  anterior,  direct  pyra- 
midal tract,  column  of  Ttirck) .  These  fibers  cross  in  the  ventral  commis- 
sure a  few  at  a  time  throughout  the  upper  levels  of  the  cord,  and  finally  ter- 
minate in  relation  with  the  motor  neurons  of  the  opposite  side.  Both  parts 
of  the  pyramidal  tract,  therefore,  decussate  before  their  fibers  terminate. 

Tractus  rubro-spinalis  (tract  of  Monakow),  from  the  nucleus  ruber  of  the 
midbrain  to  the  spinal  cord,  for  thalamic  and  cerebellar  reflexes. 

Tractus  olivo-spinahs  (Helwig's  bundle,  tractus  triangularis),  fibers  de- 
scending from  the  inferior  ohve  of  the  medulla  oblongata  to  the  lower  cer- 
vical or  upper  thoracic  segments  of  the  spinal  cord. 

Tractus  tecto-spinahs  (predorsal  bundle,  tract  of  Lowenthal),  from  the 
roof  (tectum)  of  the  midbrain  to  the  spinal  cord,  chiefly  for  optic  reflexes. 

Tractus  vestibulo-spinalis,  from  the  primary  centers  of  the  vestibular 
nerve  in  the  medulla  oblongata  to  the  spinal  cord,  for  equihbratory  reflexes. 

The  two  tracts  last  mentioned,  together  with  several  others,  compose  the 
fasciculus  marginaUs  ventralis. 

The  Fascicttltts  Propritjs 
The  fasciculus  proprius  system  of  fibers  (also  called  ground  bundles,  basis 
bundles,  and  fundamental  bundles)  comprises  chiefly  short  ascending  and 
descending  fibers  arising  from  neurons  of  the  spinal  gray  matter,  for  intrinsic 
spinal  reflexes.  In  general,  these  fibers  border  the  gray  pattern,  but  in  the 
dorsal  funiculus  some  are  aggregated  in  the  tractus  septo-marginaUs  and  the 
fasciculus  interfascicularis  (comma  tract,  tract  of  Schultze),  these  two  tracts 
also  containing  descending  branches  of  the  dorsal  root  fibers.  Some  fibers 
of  the  fasciculus  proprius  ventralis  lie  adjacent  to  the  ventral  fissure  and  are 
termed  the  fascicuhis  sulco-marginalis,  these  fibers  forming  the  direct 
continuation  into  the  cord  of  the  fasciculus  longitudinalis  medialis  (posterior 
longitudinal  bundle)  of  the  brain  (see  pp.  185,  211). 


132  INTRODUCTION  TO  NEUROLOGY 

The  sensory  nerves  which  enter  the  spinal  cord  come  either 
from  the  deep  tissues  or  from  the  skin,  and  both  of  these  types  of 
nerves  carry  fibers  of  very  diverse  functional  sorts  belonging  to 
the  somatic  sensory  group,  in  addition  to  visceral  fibers  which 
will  not  be  considered  here.  It  will  be  recalled  (see  pp.  77,  79) 
that  the  general  somatic  sensory  group  includes:  (1)  propriocep- 
tive systems,  concerned  with  motor  coordination  and  the  orien- 
tation of  the  body  and  its  members  in  space  (muscle  sense,  ten- 
don sense,  etc.),  and  (2)  exteroceptive  systems,  concerned  with 
the  relations  of  the  body  to  its  environment  (touch,  temperature, 
and  pain  sensibility).  The  first  of  these  systems  is  served 
chiefly  by  the  deep  nerves,  and  the  second  chiefly  by  the  cutane- 
ous nerves,  though  this  is  not  rigidly  true.  In  particular  it 
should  be  noted  that,  even  though  the  skin  be  completely  anes- 
thetic, the  nerves  of  deep  sensibility  can  still  respond  not  only 
to  their  proprioceptive  functions,  but  also  to  the  ordinary  clinical 
tests  for  the  exteroceptive  qualities  of  touch,  temperature,  and 
pain,  though  with  a  higher  threshold  than  in  the  case  of  the 
cutaneous  end-organs  of  these  senses. 

Henry  Head  and  his  colleagues  have  also  separated  the  cuta- 
neous fibers  into  a  protopathic  group  (including  cutaneous  pain, 
a  diffuse  non-localizable  tactile  sensibility,  and  the  discrimina- 
tion of  extreme  degrees  of  temperature)  and  an  epicritic  group 
(light  touch,  cutaneous  localization,  discrimination  of  inter- 
mediate degrees  of  temperature  and  some  others) ;  but  there  is 
difference  of  opinion  as  to  whether  these  groups  represent  two 
distinct  sets  of  nerve-fibers  or  different  stages  in  regeneration 
or  different  types  of  end-organs  of  the  same  fibers  (see  p.  84). 

Upon  entering  the  spinal  cord  all  of  these  functional  types 
of  fibers  effect  two  sorts  of  connections:  (1)  for  intrinsic  spinal 
reflexes,  and  (2)  for  the  transmission  of  their  impulses  upward  to 
the  higher  centers  of  the  brain.  We  shall  first  take  up  the  in- 
trinsic connections. 

The  simplest  of  these  intrinsic  connections  is  the  direct  motor 
reflex  illustrated  by  Fig.  1  (p.  25),  but  there  are  many  more 
complex  forms  of  the  connection  between  the  dorsal  and  ven- 
tral roots,  some  of  which  are  indicated  in  Figs.  60  and  61.  In 
general,  there  is  at  least  one  neuron  of  the  gray  matter  of  the 
spinal  cord  interpolated  between  the  dorsal  and  the  ventral  root 


THE    SPINAL    CORD    AND    ITS    NERVES 


133 


neurons,  and  usually  there  is  a  complex  chain  of  such  neurons. 
As  may  be  observed  in  Fig.  61,  the  dorsal  root  fiber  imme- 


Fig.  60. — Diagram  of  some  of  the  types  of  connection  between  the  sen- 
sory fibers  of  the  dorsal  root  and  the  motor  fibers  of  the  ventral  root  in  the 
spinal  cord  of  the  rabbit  (chiefly  after  the  researches  of  Philippson).  The 
visceral  connections  are  not  included. 

1.  Collateral  branches  of  the  dorsal  root  fibers  effect  synaptic  relations 
directly  with  dendrites  of  ventral  column  cells  of  the  same  or  the  opposite 
side. 

2.  Dendrites  of  ventral  column  cells  may  cross  to  the  opposite  side  and 
here  receive  terminals  of  dorsal  root  fibers. 

3.  A  correlation  neuron  may  be  intercalated  between  the  two  peripheral 
neurons  in  either  of  the  first  two  cases.  These  neurons  may  have  short 
axons  for  reflexes  within  a  single  segment  (3a)  or  their  axons  may  pass  out 
into  the  white  matter  (fasciculus  proprius)  and  extend  for  longer  or  shorter 
distances  in  either  the  ascending  or  the  descending  direction  (or  after  branch- 
ing in  both  directions)  for  connections  with  more  remote  motor  centers  of 
the  same  or  the  opposite  side  (36,  3c). 

4.  The  root-fibers  arising  from  the  cells  of  the'  ventral  column  themselves 
may  give  off  collateral  branches  which  return  to  the  gray  matter  and  there 
arborize  about  other  cells  of  the  ventral  column  belonging  to  different  func- 
tional groups  or  about  correlation  cells,  thus  facilitating  the  coordinated 
contraction  of  several  distinct  muscles  in  the  performance  of  some  complex 
reaction. 

The  neurons  of  the  dorsal  column  apparently  do  not  i)lay  an  imjiortant 
role  as  intercalary  elements  in  the  simpler  spinal  reflexes.  The  axons  of 
these  cells  are  for  the  most  part  directed  upward,  after  decussating  in  the 
ventral  commissure,  and  are  chiefly  concerned  with  the  transmission  of 
nervous  impulses  from  the  spinal  cord  to  the  higher  correlation  centers  of 
the  brain. 


134 


INTRODUCTION  TO   NEUROLOGY 


diately  upon  entering  the  spinal  cord  divides  into  ascending  and 
descending  branches,  and  secondary  branchlets  are  given  off  in 
large  numbers  from  each  of  these,  so  that  a  single  peripheral 
sensory  neuron  may  discharge  its  nervous  impulses  into  very 
many  central  neurons  scattered  throughout  the  entire  length  of 
the  spinal  cord.  When  to  these  numerous  endings  we  add  the 
countless  ramifications  of  the  correlation  neurons,  it  is  evident 


-spinal    lemniscus 
correlation  neuron    1 
funiculus    dorsalis 


(       )    sp.g.] 
correlation   neuron,   2 


correJation  neuron   5 


Fig.  61. — Diagram  of  the  spinal  cord  reflex  apparatus.  Some  of  the  con- 
nections of  a  single  afferent  neuron  from  the  skin  (d.r.2)  are  indicated :  d.r£, 
Dorsal  root  from  second  spinal  gangUon;?n,  muscles;  sp.g.l  to  sp.g.4,  spinal 
ganglia;  v.r.l'  to  v.r.4,  ventral  roots. 


that  even  in  the  spinal  cord,  which  is  the  simplest  part  of  the 
central  nervous  system,  there  are  reflex  mechanisms  of  great 
complexity.  Some  of  these  have  been  analyzed.  Sherrington, 
in  his  Integrative  Action  of  the  Nervous  System,  has  presented 
a  very  clear  analysis  of  the  scratch  reflex  of  the  dog  and  the 
neural  mechanisms  involved.  The  mechanism  of  the  locomotor 
reflexes  has  been  studied  physiologically  and  histologically  by 


THE    SPINAL    CORD    AND    ITS    NERVES  135 

Steincr,  Philippson,  Polimanti,  Herrick  and  Coghill,  and  very 
many  others. 

Our  most  precise  knowledge  of  the  arrangement  of  the  afferent 
and  efferent  myehnated  fibers  in  the  spinal  roots  has  been  gained 
by  the  apphcation  of  Marchi's  method  (p.  48)  to  the  study  of 
degenerations  following  accidental  and  experimental  injuries. 
Nerve-fibers  which  have  been  cut  off  from  their  cells  of  origin 
degenerate  within  about  two  weeks  after  the  injury.  It  is, 
therefore,  possible  by  the  microscopic  study  of  a  divided  nerve 
with  Marchi's  method  (which  stains  only  the  degenerating  mye- 
linated fibers)  to  determine  on  which  side  of  the  injury  are  the 
cells  of  origin  from  which  these  fibers  arise. 

Figure  62  illustrates  the  effects  of  section  of  the  spinal  roots 
made  at  four  different  places.  In  the  first  case  section  of  the 
mixed  trunk  peripherally  of  the  union  of  the  dorsal  and  ventral 
roots  is  followed  by  degeneration  of  all  of  the  myelinated  fibers 
of  the  nerve-trunk,  showing  that  the  ceU  bodies  of  all  of  these 
fibers  lie  centrally  of  the  injury.  In  the  second  case,  section  of 
the  ventral  root  close  to  the  spinal  cord  is  followed  by  degenera- 
tion of  all  the  fibers  of  this  root  without  disturbance  of  those 
of  the  dorsal  root,  showing  that  the  ventral  root  fibers  arise  as 
axons  of  cells  within  the  spinal  cord.  In  the  third  case  section 
of  the  dorsal  root  fibers  peripherally  of  the  ganglion  and  before 
their  union  with  those  of  the  ventral  root  results  in  the  degenera- 
tion of  all  of  the  fibers  of  the  mixed  nerve  which  arise  in  the 
spinal  ganghon  (sensory  fibers),  without  loss  of  any  motor  fibers 
from  the  ventral  root.  In  the  fourth  case  section  of  the  dorsal 
root  on  the  central  side  of  the  ganglion  is  followed  by  degenera- 
tion of  all  myelinated  fillers  of  the  central  stump  of  this  root,  Ixit 
not  of  the  peripheral  part  of  the  root  or  the  spinal  ganglion. 
This  shows  that  the  cells  of  origin  of  these  fibers  lie  in  the  spinal 
ganglion  and  not,  like  those  of  the  ventral  root,  within  the  spinal 
cord.  The  peripheral  processes  of  these  ganglion  cells,  there- 
fore, are  dendrites,  and  the  centrally  directed  processes  which 
compose  the  dorsal  roots  are  axons  (cf.  Fig.  1,  p.  25,  and  Fig. 
56,  p.  126). 

Another  useful  method  for  the  solution  of  problems  of  this 
character  is  the  study  of  the  fine  structure  of  the  cell  bodies  of 
the  neurons  after  such  experimental  lesions  as  those  just  des- 


136 


INTRODUCTION   TO   NEUROLOGY 


cribed.  Neurons  whose  peripheral  fibers  have  been  severed, 
thus  cutting  the  cell  body  off  from  its  usual  avenue  of  functional 
discharge,  within  a  few  days  thereafter  undergo  structural 
changes,  chief  of  which  is  chromatolysis,  or  the  solution  and  dis- 
appearance of  the  Nissl  bodies  (see  p.  49).    Thus,  after  cutting 


m 


EZ 


Fig.  62. — Four  sketches  to  illustrate  the  degenerations  of  somatic  sensory 
and  motor  fibers  which  follow  section  of  spinal  nerve-roots  in  different  places. 
Fibers  separated  from  their  cells  of  origin  will  degenerate,  as  shown  in  black 
(see  the  text,  p.  135). 


a  ventral  spinal  root  (Fig.  62,  II),  a  microscopic  examination  of 
the  spinal  cord  will  show  the  chromatolysis  effect  (see  Fig.  13, 
p.  48)  in  every  neuron  in  the  ventral  gray  column  which  gives 
rise  to  a  fiber  of  this  root,  while  all  of  the  other  neurons  will 
remain  normal. 

Physiological  experiments  upon  men  and  other  animals  where 


THE    SPINAL    CORD    AND    ITS    NERVES  137 

such  injuries  have  taken  place  give  the  necessary  control  to  con- 
firm the  proof  that  efferent  fibers  leave  the  spinal  cord  through 
the  ventral  roots  and  afferent  fibers  enter  through  the  dorsal 
roots,  for  the  loss  of  ventral  roots  results  in  a  motor  paralysis  of 
the  muscles  supplied  by  them,  while  the  destruction  of  dorsal 
roots  results  in  the  loss  of  superficial  and  deep  sensibility  in  the 
regions  innervated,  with  no  loss  of  motor  function  save  for  the 
imperfect  coordination  resulting  from  the  loss  of  the  sensory 
control  through  the  proprioceptive  system  (ataxia). 

Turning  now  to  the  conduction  paths  between  the  spinal 
cord  and  the  brain,  we  notice  first  that  the  reactions  involved 
here  may  be  performed  either  reflexly  or  consciously.  In  the 
latter  case  a  connection  with  the  cerebral  cortex  is  to  be  expected; 
in  the  former  case  an  infinite  variety  of  reflex  connections  within 
the  brain  stem  is  possible. 

The  sensory  or  ascending  fibers  which  pass  between  the 
spinal  cord  and  the  brain  may  be  classified  as  follows: 

I.  Proprioceptive  systems: 

1.  To  the  cerebellum  (unconscious). 

2.  To  the  brain  stem  (unconscious). 

3.  To  the  thalamus  and  cerebral  cortex  (sensations  of  posture  and 

spatial  adjustment). 

II.  Exteroceptive  systems: 

1.  To  the  brain  stem  (unconscious). 

2.  To  the  thalamus  and  cerebral  cortex  (sensations  of  touch,  tempera- 

ture, and  pain) . 

I.  Proprioceptive  Systems. — As  soon  as  the  afferent  fibers  of 
the  spinal  nerves  have  entered  the  spinal  cord  they  are  im- 
mediately segregated  into  proprioceptive  and  exteroceptive 
groups,  as  suggested  by  the  analysis  above  (see  Figs.  63,  64,  81, 
and  83).  The  proprioceptive  fibers  take  quite  different  courses, 
depending  upon  whether  they  are  directed  into  the  cerebellar 
path  or  into  the  path  to  the  brain  stem  and  cerebral  cortex. 
Some  terminals  of  this  system  end  in  the  gray  matter  between  the 
dorsal  and  ventral  columns  (the  nucleus  dorsahs  of  Clarke,  or 
Clarke's  column,  and  adjacent  regions),  whose  neurons  send  their 
axons  into  the  dorsal  and  ventral  spino-cerebellar  tracts  and 
finally  into  the  cerebellum.  The  cerel^ellum  is  the  great  center 
of  motor  coordination,  and  these  spino-cerebellar  tracts  are  two 


138  INTRODUCTION  TO  NEUROLOGY 

only  out  of  a  larger  number  of  paths  by  which  afferent  spinal 
impulses  may  be  discharged  into  it  (see  p.  188). 

The  remaining  proprioceptive  fibers  of  the  spinal  roots  are 
directed  upward  in  the  dorsal  funiculus,  of  which  they  form  the 
larger  part.  At  the  point  where  the  spinal  cord  passes  over 
into  the  medulla  oblongata  they  terminate,  and  after  a  synapse 
here  the  neurons  of  the  second  order  carry  the  impulse  across  to 
the  opposite  side  of  the  brain  and  upward  toward  the  thalamus 
in  a  tract  known  as  the  medial  lemniscus  or  fillet  (Fig.  64). 
After  another  synapse  here,  a  final  neuron  may  carry  the  nervous 
impulse  forward  to  the  cerebral  cortex.  This  medial  lemniscus 
system  is  largely  concerned  with  unconscious  motor  adjustments 
involving  the  muscles  of  the  trunk  and  limbs.  Disturbance  of 
its  functions  produces  motor  incoordination  (ataxia),  but  not 
necessarily  any  great  loss  of  exteroceptive  sensations.  So  far  as 
its  functions  come  into  consciousness,  they  are  recognized  as  sen- 
sations of  position,  spatial  localization,  and  motor  control. 

II.  Exteroceptive  Systems. — The  central  course  of  the  extero- 
ceptive fibers  of  the  spinal  nerves  is  quite  different  from  that 
just  described.  Almost  immediately  after  entering  the  spinal 
cord  these  fibers  terminate  among  the  neurons  of  the  dorsal 
gray  column.  After  a  synapse  here  the  fibers  of  the  second  order 
cross  to  the  opposite  side  of  .-^he  spinal  cord,  and  here  turn  and 
ascend  in  the  white  matter  of'  the  lateral  and  ventral  funiculi, 
where  they  form  the  spinal  lemniscus,  or  tractus  spino-thalamicus. 
Some  fibers  of  the  spinal  lemniscus  ascend  throughout  the  entire 
length  of  the  spinal  cord,  medulla  oblongata,  and  midbrain,  to 
end  in  the  thalamus.  In  the  upper  part  of  their  course  these 
fibers  accompany  those  of  the  medial  lemniscus  already  des- 
cribed. 

Collateral  connections  are  effected  between  the  ascending 
fibers  of  the  spinal  lemniscus  and  the  various  motor  nuclei  of  the 
brain  for  different  cranial  reflexes,  such  as  turning  the  eyes  in 
response  to  a  cutaneous  stimulation  on  the  hand.  But  their 
final  terminus  is  in  the  thalamus,  and  after  a  synapse  here  the 
nervous  impulse  may  be  carried  forward  to  the  cerebral  cortex 
by  neurons  of  the  third  order.  The  spinal  lemniscus  system  is 
the  chief  ascending  pathway  for  nervous  impulses  giving  rise  to 
consciousness  of  touch,  temperature,  and  pain  from  the  trunk 


THE    SPINAL    CORD    AND    ITS    NERVES 


139 


and  limbs.  There  is  a  similar  but  anatomically  distinct  path- 
way to  the  thalamus  for  cutaneous  sensibility  from  the  head, 
which  is  called  the  trigeminal  lemniscus  (see  p.  180  and  Figs. 
64,  77,  81). 

Within  the  spinal  cord  the  nerve-fibers  of  sensibility  to  pres- 
sure, pain,  and  temperature  run  in  three  distinct  tracts  of  the 

■Fasciculus  gracilis    1 

„     .    ,  ^     l- proprioceptive 

Fasciculus  cuneatusj 

Dorsal  spino-cere- 
bellar  tract  (pro- 
prioceptive) 

Nucleus  dorsalis  of 
Clarke 

Ventral  spino-cere- 
bellar  tract  (pro- 
prioceptive) 

Spinal  lemniscus 
(exteroceptive  for 
pain,    heat,    and 
cold) 

Spinal  lemniscus 
(exteroceptive  for 
touch   and   pres- 
sure) 

Fig.  63. — Diagram  to  illustrate  the  terminations  within  the  spinal  cord 
of  some  of  the  types  of  somatic  sensory  fibers  and  their  secondary  paths. 
The  central  connections  of  root  fibers  1,  2,  and  .5  provide  for  proprioceptive 
responses;  those  of  fibers  .3  and  4,  for  exteroceptive  responses.  Root  fiber 
1  terminates  in  the  nucleus  of  the  fasciculus  cuneatus  of  the  same  side  at 
the  upper  end  of  the  spinal  cord  and  conveys  impulses  of  muscular  sensi- 
bility, sense  of  passive  position  and  movement,  and  of  spatial  discrimina- 
tion. Root  fiber  2  terminates  in  the  nucleus  dorsalis  of  Clarke  (Clarke's 
column)  and  root  fiber  5  in  the  same  nucleus  or  adjacent  parts  of  the  gray 
substance.  These  fibers  call  forth  unconscious  cerebellar  activity  underly- 
ing the  coordination  and  reflex  tone  of  the  muscles.  Root  fibers  3  and  4 
terminate  in  the  dorsal  gray  column  and  convey  exteroceptive  impulses. 
Fiber  3  typifies  all  fibers  which  carry  sensibility  of  pain,  heat,  and  cold; 
fiber  4,  those  which  carry  sensibility  of  touch  and  pressure. 


spinal  lemniscus  (the  pain  and  temperature  tracts  very  close 
together,  see  Figs.  59,  63,  and  81),  so  that  it  occasionally  hap- 
pens that  one  may  be  destroyed  by  accident  or  disease  without 
affecting  the  other  two.  Thus,  at  the  level  of  the  fifth  cervical 
vertebra  the  destruction  of  the  pathway  for  touch  and  pressure 
(tractus  spino-thalamicus  ventralis  of  Fig.  59)  would  result  in 
the  total  loss  of  both  cutaneous  and  deep  sensibility  to  pressure 


140  INTRODUCTION  TO  NEUROLOGY 

over  the  whole  of  the  opposite  side  of  the  body  below  the  level 
of  the  injury,  but  there  would  be  no  disturbance  of  either  tem- 
perature or  pain  sensibility.  Similarly,  by  an  injury  of  the  trac- 
tus  spino-thalamicus  lateralis,  pain  or  temperature  sensibility 
might  be  lost  with  no  disturbance  of  pressure  sense.  (For  the 
description  of  a  case  of  this  sort  see  p.  173.) 

Such  combinations  of  symptoms  as  just  described  could 
not  occur  from  any  form  of  injury  to  the  peripheral  nerves,  for 
in  these  nerves  the  various  kinds  of  fibers  are  all  mingled  in  the 
larger  trunks,  so  that  one  functional  component  cannot  be  in- 
jured without  involvement  of  the  others  also.  And  at  the  first 
division  of  these  trunks  into  deep  and  superficial  branches  each 
branch  also  carries  all  or  nearly  all  of  the  functional  systems 
(see  pp.  79-84,  132). 

The  return  pathway  for  motor  nervous  impulses  from  the 
cerebral  cortex  is  the  cortico-spinal  tract  or  pyramidal  tract 
(Fig.  64),  whose  fibers  descend  without  interruption  from  the 
precentral  gyrus  of  the  cerebral  cortex  (see  p.  283)  to  the  spinal 
cord,  where  they  form  the  lateral  and  ventral  cortico-spinal 
tracts  (Fig.  59).  The  various  reflex  centers  of  the  brain  stem 
also  send  motor  fibers  downward  into  the  cord  for  the  excitation 
of  movements  of  the  trunk  and  limbs.  The  tecto-spinal  tract 
(Fig.  59)  is  such  a  path,  leading  from  the  optic  and  acoustic 
centers  of  the  midbrain,  as  is  also  the  vestibulo-spinal  tract, 
leading  from  the  vestibular  nuclei  of  the  medulla  oblongata 
(p.  176,  Fig.  83,  neuron  16). 

Summary.— The  spinal  nerves  are  segmentally  arranged  and 
are  named  after  the  vertebrae  adjacent  to  which  they  emerge 
from  the  spinal  canal  of  the  vertebral  column.  Each  nerve 
arises  by  a  series  of  dorsal  rootlets  afferent  in  function  and  a 
series  of  ventral  rootlets  efferent  in  function.  Most  of  the  gray 
matter  of  the  spinal  cord  is  massed  in  two  longitudinal  columns 
on  each  side,  for  somatic  sensory  and  somatic  motor  functions 
respectively.  These  are  separated  by  an  intermediate  region 
containing  the  visceral  sensory  and  motor  centers  and  various 
correlation  neurons.  The  white  matter  of  the  cord  is  superficial 
to  the  gray  and  contains  myelinated  fibers  for  various  kinds  of 
correlation,  besides  root-fibers  of  the  spinal  nerves.  The  white 
matter  is  divided  topographically  into  funiculi  and  fasciculi  and 


THE    SPINAL    CORD    AND    ITS    NERVES 


141 


physiologically  into  tracts.  The  latter  are  the  really  significant 
units  in  the  analysis  of  the  cord.  Peripherally,  the  spinal  nerves 
divide  into  deep  and  superficial  branches,  and  the  latter  contain, 


cerebral 


cortex 


trigeminal   lemniscus 
sKin 


ventral  pyramidal 
Tract 


nucleus  of  dorsal 

funiculus 


dorsal  funiculus 
lateral  pyramidal  tract 
spinal  ganglion 
sKin 

muscle 

Fig.  64. — Diagram  of  the  chief  connections  between  the  spinal  cord  and 
the  cerebral  cortex.  The  spinal  lemniscus  complex  carries  the  ascending 
exteroceptive  systems  (touch,  temperature,  and  pain) ;  the  dorsal  funiculus 
and  medial  lemniscus  complex  carries  chiefly  ascending  proprioceptive  sys- 
tems (a  nerve  of  muscle  sense  is  the  only  member  of  this  gi'oup  included 
in  the  drawing).  The  diagram  also  includes  the  sensory  path  from  the  skin 
of  the  head  to  the  cerebral  cortex  through  the  V  cranial  nerve  (trigeminus) 
and  the  trigeminal  lemniscus  (p.  157).  The  pyramidal  tract  (tractus  cor- 
tico-spinahs)  is  the  common  descending  motor  path  for  both  exteroceptive 
and  proprioceptive  nervous  impulses  from  the  cerebral  cortex. 


142  INTRODUCTION  TO  NEUROLOGY 

according  to  Henry  Head,  protopathic  and  epicritic  functional 
systems  of  fibers.  As  soon  as  the  peripheral  nerve-fibers  have 
entered  into  the  spinal  cord  they  are  segregated  into  proprio- 
ceptive and  exteroceptive  groups,  and  each  of  these  again  into 
particular  functional  tracts.  There  are  connections  for  local 
spinal  reflexes,  reflexes  of  the  brain  stem  and  cerebellum,  and 
for  the  cerebral  cortex.  The  spino-cerebellar  tracts  and  the 
dorsal  funiculi  are  proprioceptive  in  function,  and  the  spinal 
lemniscus  carries  spino-thalamic  tracts  of  the  systems  of  touch, 
temperature,  and  pain  sensibility  for  the  cerebral  cortex. 

Literature 

Barker,  L.  F.  1901.  The  Nervous  System  and  Its  Constituent  Neu- 
rones, New  York. 

Brotjwer,  B.  1915.  Die  biologische  Bedeutung  der  Dermatomerie. 
Beitrag  zur  Kenntnis  der  Segmentalanatomie  und  der  Sensibilitatsleitung 
im  Rlickenmark  und  in  der  Medulla  Oblongata,  Folia  Neuro-biologica,  Bd. 
9,  pp.  225-336. 

Bruce,  A.  1901.  A  Topographic  Atlas  of  the  Spinal  Cord,  London. 

Bruce,  A.  N.  1910.  The  Tract  of  Gowers,  Quart.  Journ.  Exp.  Physiol, 
vol.  iii,  pp.  391^07. 

Head,  H.,  Rivers,  W.  H.  R.,  and  Sherren,  J.  1905.  The  Afferent 
Nervous  System  from  a  New  Aspect,  Brain,  vol.  xxviii,  pp.  99-115. 

Head,  H.,  and  Thompson,  T.  1906.  The  Grouping  of  the  Afferent 
Impulses  Within  the  Spinal  Cord,  Brain,  vol.  xxix,  p.  537. 

Herrick,  C.  Judson,  and  Coghill,  G.  E.  1915.  The  Development  of 
Reflex  Mechanisms  in  Amblystoma,  Jour.  Comp.  Neur.,  vol.  xxv,  pp.  65-85. 

Philippson,  M.  1905.  L'autonomie  et  la  centralisation  dans  le  systeme 
nerveux  des  animaux,  Paris. 

PoLiMANTi,  O.  1911.  Contributi  aUa  fisiologia  del  sistema  nervoso  cen- 
trale  e  del  movimento  dei  pesci,  Zool.  Jahrb.,  Abt.  f.  Zool.  u.  Physiol.,  Bd. 
30,  pp.  473-716. 

Rivers,  W.  H.  R.,  and  Head,  H.  1908.  A  Human  Experiment  in  Nerve 
Division,  Brain,  vol.  xxxi,  p.  32.3. 

Sherrington,  C.  S.  1906.  The  Integrative  Action  of  the  Nervous  Sys- 
tem, New  York. 

Steiner,  J.  1885.  Die  Functionen  des  Centralnervensystems  und  ihre 
Phylogenese.  I.  Abteilung.  Untersuchungen  iiber  die  Physiologie  des 
Froschhirns,  Braunschweig. 

— .  1888.  Idem.  11.  Abteilung,  Die  Fische. 

_ — .    1900.    Idem.  IV.  Abteilung,    Reptilien-Ruckenmarksreflexe,  Ver- 
mischtes. 

— .  1886.  Ueber  das  Centralnervensystem  der  griinen  Eidechse  nebst 
weiteren  Untersuchungen  iiber  das  des  Haifisches,  Sitzb.  k.  Akad.  Wiss., 
BerUn,  p.  541. 


CHAPTER  IX 

THE    MEDULLA    OBLONGATA    AND    CEREBELLUM 

The  brain  contains  a  series  of  primary  sensory  and  motor 
centers  related  to  the  cranial  nerves  (see  p.  109),  the  correlation 
mechanism  which  serves  these  sensori-motor  centers,  and  an 
extensive  system  of  conduction  pathways  between  the  brain  and 
spinal  cord  and  between  the  various  correlation  centers  of  the 
brain  itself. 

The  brain  is  divided  into  two  principal  parts  by  a  constriction 
in  front  of  the  cerebellum  and  pons,  the  isthmus  (see  p.  122). 
Above  this  level  lies  the  cerebrum  and  below  it  the  rhomben- 
cephalon, comprising  the  medulla  oblongata  or  bulb  and  the 
cerebellum.  The  medulla  oblongata  contains  the  primary 
centers  concerned  with  most  of  the  simpler  cerebral  reflexes, 
especially  those  of  the  visceral,  general  cutaneous,  auditory,  and 
proprioceptive  systems  (see  pp.  112  and  123).  The  cerebellum 
is  a  suprasegmental  apparatus  developed  phylogenetically  and 
embryologically  out  of  the  more  primitive  bulbar  nuclei  of  the 
vestibular  nerve,  i.  e.,  out  of  the  acoustico-lateral  area  of  fishes 
(Figs.  43  and  44,  pp.  Ill,  112,  and  Fig.  68). 

The  olfactory  nerve  (I  pair),  the  so-called  optic  nerve  (II 
pair),  and  the  auditory  nerve  (VIII  pair)  are  special  sensory 
nerves,  whose  central  connections  will  be  described  more  in 
detail  below.  The  remaining  nine  pairs  of  cranial  nerves  of  the 
human  body  may  be  briefly  summarized  as  follows: 

The  oculomotor  nerve  (III  pair),  trochlear  nerve  (IV  pair),  and  abducens 
(VI  pair)  contain  the  somatic  motor  fibers  and  fibers  of  muscle  sense  related 
to  the  six  muscles  which  move  the  eyeball.  The  III  pair  also  contains  vis- 
ceral motor  fibers  for  the  ciliary  ganglion,  from  which  are  innervated 
the  muscles  of  the  ciliary  process  and  iris  within  the  eyeball,  i.  c,  the  muscles 
of  accommodation.  The  trigeminal  nerve  (V  pair)  supplies  general  sensibil- 
ity to  the  skin  and  deep  tissues  of  the  face  and  the  motor  innervation  of  the 
muscles  of  mastication.  The  facial  nerve  (VII  ]xiir)  innervates  the  taste- 
buds  of  the  anterior  two-thirds  of  the  tongue  (special  visceral  sensory  fibers), 
the  subhngual  and  submaxillary  salivary  glands  (general  visceral  efferent 

143 


144  INTRODUCTION  TO  NEUROLOGY 

fibers),  and  the  muscles  related  with  the  hyoid  bone  and  the  superficial 
facial  muscles  or  muscles  of  facial  expression,  these  two  groups  of  muscles 
belonging  to  the  series  of  special  visceral  muscles  (p.  94).  The  glosso- 
pharyngeal nerve  (IX  pair)  supphes  fibers  to  the  taste-buds  on  the  posterior 
third  of  the  tongue  (special  visceral  sensory),  also  general  sensibihty  to  this 
region,  motor  fibers  for  the  stylopharyngeus  muscle  (special  visceral  motor), 
and  excito-glandular  fibers  for  the  parotid  sahvary  gland  (general  visceral 
efferent) .  It  also  cooperates  with  the  vagus  nerve  in  innervating  the  skin 
about  the  external  auditory  canal  (by  the  auricular  branch  of  the  vagus). 
The  vagus  nerve  (X  pair)  is  very  complex.  In  addition  to  the  general  so- 
matic sensory  fibers  of  the  auricular  branch,  which  have  just  been  men- 
tioned, it  contains  general  visceral  sensory  fibers  from  the  pharynx,  lungs, 
stomach,  and  other  abdominal  viscera,  and  visceral  efferent  fibers  of  several 
sorts  to  the  pharynx,  esophagus,  stomach,  intestines,  lungs,  heart,  and 
arteries.  The  peripheral  and  central  courses  of  most  of  these  fimctional 
systems  have  been  accurately  determined,  but  are  far  too  complex  for  sum- 
mary here.  The  accessory  nerve  (XI  pair)  contains  two  parts:  (1)  the 
bulbar  part,  which  should  be  regarded  as  nothing  other  than  detached 
filaments  of  the  vagus,  for  all  of  these  fibers  peripherally  join  vagus  branches, 
(2)  the  spinal  part,  which  arises  by  numerous  rootlets  from  the  upper  levels 
of  the  spinal  cord  and  participates  in  the  innervation  of  two  of  the  muscles 
of  the  shoulder  (the  trapezius  and  sternocleidomastoid  muscles) .  The  hu- 
man hypoglossus  nerve  (XII  pair)  is  a  modified  derivative  of  the  first  spuial 
nerve  of  lower  vertebrates.  It  has  lost  its  sensory  fibers  and  innervates 
a  special  part  of  the  tongue  musculature. 

All  of  the  nerves  of  the  preceding  list  except  the  I,  II,  III,  and 
IV  pairs  connect  with  the  medulla  oblongata.  In  the  dogfish 
we  have  seen  that  this  region  of  the  brain  presents  special  emi- 
nences which  form  respectively  the  terminal  nuclei  of  the 
acoustic  (and  lateral  line),  cutaneous,  and  visceral  (including 
gustatory)  sensory  systems  (see  p.  112  and  Figs.  42-44).  The 
primary  motor  centers  lie  ventrally  of  these  sensory  areas. 

The  cranial  nerves  are  usually  described  in  our  text-books 
as  if  they  were  segmental  units  like  the  spinal  nerves  (see  p. 
125).  This  was,  in  fact,  the  primitive  condition;  but  in  all 
vertebrate  animals  this  segmental  pattern  has  been  greatly 
modified  in  such  a  way  as  to  facilitate  the  discharge  into  the 
brain  of  all  sensory  fibers  of  hke  physiological  type  into  a  single 
center.  These  physiological  systems  are/accordingly,  the  most 
useful  units  of  structure  in  the  cranial  nerves.  Each  cranial 
nerve  may  contain  several  of  these  functional  systems,  and  no 
two  pairs  of  cranial  nerves  have  the  same  composition.  The 
components  of  the  cranial  nerves,  like  those  of  the  spinal  nerves 
(p.  126),  are  named  in  accordance  with  the  same  physiological 
criteria  as  their  end-organs  (see  pp.  79-94). 


THE  MEDULLA  OBLONGATA  AND  CEREBELLUM  '    145 

A  functional  system  may  be  defined  as  the  sum  of  all  the 
neurons  in  the  body  which  possess  certain  physiological  and 
anatomical  characters  in  common  so  that  they  may  react  in  a 
common  mode.  Morphologically,  each  system  of  peripheral 
nerves  is  defined  by  the  terminal  relations  of  its  fibers — by  the 
organs  with  which  they  are  related  peripherally  and  by  the 
centers  in  which  the  fibers  arise  or  terminate.  A  single  periph- 
eral nerve  may  contain  several  of  these  systems.  It  becomes 
necessary,  therefore,  to  analyze  the  root  complex  of  each  pair  of 
spinal  and  cranial  nerves  into  its  components,  and  to  trace  not 
only  the  central  connections  of  these  components  within  the 
spinal  cord  and  brain,  but  also  their  peripheral  courses  as  well. 
In  other  words,  the  description  of  any  given  nerve  or  ramus  is  not 
complete  when  we  have  given  its  point  of  origin  from  the  nerve- 
trunk,  root,  or  ganglion,  the  details  of  its  devious  courses,  and 
the  exact  points  where  the  several  ramuli  terminate.  In  addi- 
tion to  this  it  is  necessary  to  learn  what  functional  systems  are 
represented  in  each  ramus  and  the  precise  central  and  peripheral 
relations  of  each  system. 

Each  of  the  four  primary  divisions  of  the  spinal  nerves 
(somatic  sensory  and  motor,  visceral  sensory  and  motor,  see 
p.  126)  is  represented  in  the  head  region  in  the  same  primitive 
unspecialized  form  as  seen  in  the  spinals,  and  also  by  specialized 
systems  found  only  in  one  or  more  cranial  nerves.  This  gives 
eight  groups  of  functional  systems  represented  in  the  cranial 
nerves,  as  follows: 

1.  General  somatic  afferent  nerves,  supplying  (1)  general  exteroceptive 
sensibility  to  the  skin  and  the  underlying  tissues,  and  (2)  deep  propriocep- 
tive sensibility  to  the  muscles,  tendons,  etc.  Type  1  is  represented  in  the 
V,  IX,  and  X  nerves,  and  in  some  lower  vertebrates  in  the  VII  nerve  also 
(there  is  some  clinical  evidence  for  its  presence  in  the  VII  nerve  of  man); 
type  2  is  represented  in  the  III,  IV,  V,  VI  nerves  and  probably  in  some  of 
the  others  also. 

2.  Special  somatic  afferent  nerves,  for  the  innervation  of  highly  differ- 
entiated sense  organs.  Here  belong  in  the  exteroceptive  series  the  coch- 
lear branch,  and  in  the  proprioceptive  series  the  vestibular  branch  of  the 
VIII  pair.  The  lateral  line  nerves  of  fishes  belong  here,  and  probabh'  the 
visual  organ  connected  with  the  II  pair  in  all  vertebrates  (though  the  so- 
called  optic  nerve  is  not  a  true  nerve,  see  p.  204). 

3.  General  somatic  efferent  nerves,  supplying  the  general  skeletal  muscu- 
lature of  the  body.  In  fishes  this  system  is  represented  in  several  cranial 
nerves  in  addition  to  the  spinalis,  but  in  man  it  is  lost  in  the  cranial  nerves, 
unless,  as  some  beUeve,  a  part  of  the  fibers  of  the  XI  pair  belong  here. 

10 


146 


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148  INTRODUCTION  TO  NEUROLOGY 

4.  Special  somatic  efferent  nerves,  supplying  two  groups  of  highly  special- 
ized somatic  muscles,  namely,  the  external  eye  muscles  and  a  part  of  the 
tongue  muscles.  They  arise  from  a  ventro-medial  series  of  motor  nuclei  and 
are  represented  in  the  III,  IV,  VI,  and  XII  pairs. 

5.  General  visceral  afferent  nerves,  innervating  visceral  mucous  surfaces 
without  highly  differentiated  sense  organs.  They  distribute  through  the 
sympathetic  nervous  system  and  are  represented  in  the  VII,  IX,  and  X  pairs 
and  perhaps  in  some  others. 

6.  Special  visceral  afferent  nerves,  for  the  innervation  of  specialized  sense 
organs  serving  the  senses  of  taste  and  smell.  The  gustatory  fibers  are 
represented  in  the  VII,  IX,  and  X  pairs.  The  olfactory  nerve  (I  pair)  is 
probably  a  more  highly  differentiated  member  of  this  group  (see  pp.  91 
and  215). 

7.  General  visceral  efferent  nerves,  for  unstriped  involuntary  visceral 
muscles,  heart  muscle,  glands,  etc.,  distributing  through  the  sympathetic 
nervous  system.  These  fibers  (preganglionic  fibers  of  Langely,  p.  229)  are 
present  in  the  III,  VII,  IX,  X,  and  XI  pairs. 

8.  Special  visceral  efferent  nerves,  supplying  highly  specialized  striated 
muscles  of  a  different  origin  (both  embryologically  and  phylogenetically) 
from  the  striated  trunk  muscles.  These  muscles  are  connected  with  the 
visceral  or  facial  skeleton  of  the  head  and  are  derived  from  the  gill  muscles 
of  fishes.  These  nerves  in  the  adult  body  resemble  those  of  the  somatic 
motor  system,  save  that  they  arise  from  a  different  series  of  motor  nuclei  in 
the  brain  (the  ventro-lateral  motor  column) .  They  have  no  connection  with 
the  sympathetic  nervous  system  and  are  represented  in  the  V,  VII,  IX,  X, 
and  XI  pairs. 

In  the  preceding  Table  of  Nerve  Components  (pages  146,  147)  the  sev- 
eral cranial  nerves  are  analyzed  and  compared  with  a  typical  spinal  nerve. 

The  various  functional  systems  of  the  head  tend  to  be  con- 
centrated in  one  or  a  few  cranial  nerves  for  ease  of  central  corre- 
lation, and  even  in  case  a  given  system  is  represented  in  several 
nerves,  the  fibers  of  this  system  may  converge  within  the  brain 
to  connect  with  a  compact  center.  This  is  well  illustrated  by  the 
gustatory  and  acoustico-lateral  systems  of  the  cranial  nerves  of 
the  fish,  Menidia,  as  shown  in  Fig.  65.  Here  the  gustatory  sys- 
tem (indicated  by  cross-hatching)  is  present  in  the  VII,  IX,  and 
X  cranial  nerves,  and  all  of  these  fibers,  together  with  other 
visceral  fibers,  converge  within  the  brain  to  enter  the  visceral  sen- 
sory area  in  the  vagal  lobe  (lob.X.).  Similarly,  the  lateral  line 
components  of  the  VII  and  X  nerves  and  the  VIII  (printed  in 
solid  black)  converge  to  enter  the  acoustico-lateral  area  in  the 
tuberculum  acusticum  (t.a.).  The  general  cutaneous  fibers 
enter  by  the  V  and  X  nerves,  and  all  of  these  fibers  enter  the 
spinal  V  tract  (sp.V.). 

In  the  paragraphs  which  follow  the  chief  central  connections  (terminal 
nuclei  of  the  sensory  systems  and  nuclei  of  origin  of  the  motor  systems,  see 


THE  MEDULLA  OBLONGATA  AND  CEREBELLUM 


149 


p.  108)  of  some  of  the  cranial  nerve  components  are  smnmarized  (see  Fig. 
71).  For  the  details  of  these  connections  the  larger  text-books  of  neurology 
should  be  consulted. 

1.  General  Cutaneous  System  (part  of  the  general  somatic  afferent,  repre- 
sented in  the  V,  IX,  and  X  nerves). — Chief  sensory  V  nucleus  and  spinal 
V  nucleus,  or  gelatinous  substance  of  Rolando  of  the  medulla  oblongata. 


rAniesi 


Fig.  65. — A  diagram  of  the  sensory  components  of  the  cranial  nerves  of  a 
fish,  Menidia.  The  brain  is  outlined  as  seen  from  the  right  side  with  heavy 
black  lines.  The  general  cutaneous  nerves  (somatic  sensory)  are  outUned 
with  finer  Hues  (unshaded),  and  all  of  these  fibers  are  seen  to  enter  a  longi- 
tudinal tract  within  the  brain,  the  spinal  trigeminal  tract  (sp.V.).  The 
special  somatic  sensory  (acoustic  and  lateral  line)  nerves  (black)  converge 
within  the  brain  to  a  special  center,  the  acoustico-lateral  area,  or  tuberculum 
acusticum  (t.a.).  The  visceral  sensory  fibers  (cross-hatched)  Likewise  all 
converge  to  a  special  center,  the  lobus  vagi  (lob.X.). 

Reference  letters:  b.c.l  to  b.c.5,  gill  clefts;  br.g.X.,  branchial  ganglia  of 
X  nerve;  dig.,  ciliary  ganglion;  d.Z. (7. F77.,  dorsal  lateral  line  ganglion  of  VII 
nerve;  f.c,  fasciculus  sohtarius;  gen.g.VII.,  geniculate  ganglion  of  VII 
nerve;  IX.,  glossopharyngeal  nerve;  jug.g.,  jugular  ganglion  of  X  nerve; 
lob.X.,  lobus  vagi  (visceral  sensory  area);  n.L,  olfactory  nerve;  n.IL,  optic 
nerve;  n.III.,  oculomotor  nerve;  o.pr.,  ramus  ophthahnicus  profundus;  pal., 
palatine  branch  of  VII  nerve;  r.cut.dors.X.,  dorsal  cutaneous  branch  of  X 
nerve;  r.intcst.X.,  intestinal  branch  of  X  nerve;  r.lat.ac.,  ramus  lateralis  ac- 
cessorius  of  VII  nerve;  r.lat.X.,  lateral  line  branch  of  X  nerve;  r.oph.sup.V 
+  VII.,  superficial  ophthalmic  branch  of  V  and  VII  nerves;  r.o^,  ramus 
oticus;  r.st.X.,  supratemporal  branch  of  X  nerve;  r.VII.p-t.,  jiretromatic 
branch  of  VII  nerve;  sp.V.,  spinal  trigeminal  tract;  /.a.,  tuberculum  acusti- 
cum (acoustico-lateral  area);  t.fmi.,  hyomandibular  trunk;  t.inf.,  infra- 
orbital trunk;  VIII.,  auditory  nerve;  v.l.g.VIL,  ventral  lateral  Une  gan- 
glion of  VII  nerve. 


150  INTRODUCTION  TO  NEUROLOGY 

2.  Special  Somatic  Afferent  Systems. — (1)  Vestibular  nuclei;  (2)  cochlear 
nuclei;  (3)  optic  tectum  in  the  colUculus  superior,  optic  part  of  the  thala- 
mus (lateral  geniculate  body  and  pulvinar). 

3.  General  Somatic  Efferent  System. — Not  represented  in  the  human 
cranial  nerves. 

4.  Special  Somatic  Efferent  Systems  (III,  IV,  VI,  and  XII  nerves). — 
A  series  of  ventral  motor  nuclei  in  the  midbrain  and  medulla  oblongata. 

5  and  6.  General  and  Special  Visceral  Afferent  Systems  (VII,  IX,  and  X 
nerves). — All  of  the  fibers  concerned  with  general  visceral  sensibility  and 
taste  enter  a  single  longitudinal  tract,  the  fasciculus  solitarius,  and  termin- 
ate in  the  nucleus  which  accompanies  this  fasciculus.  (The  olfactory  nerve 
and  its  cerebral  centers  probably  should  also  be  included  here.) 

7.  General  Visceral  Efferent  Systems  (III,  VII,  IX,  X,  and  XI  nerves). — 
These  are  preganglionic  fibers  of  the  sympathetic  system  and  arise  from 
laterally  placed  nuclei  (except  that  of  the  III  nerve,  which  is  joined  to  the 
ventral  somatic  motor  nucleus). 

8.  Special  Visceral  Efferent  Systems  (V,  VII,  IX,  X,  and  XI  nerves). 
— A  series  of  lateral  motor  nuclei  of  the  medulla  oblongata. 

The  spinal  nerves,  as  we  have  seen,  enter  the  spinal  cord  by  a 
series  of  segmentally  arranged  roots.     Within  the  spinal  cord, 


Somatic  sensory  column 

_        ,  Dorsal  funiculus 

Visceral  sensory  column 

,r-         .  ,  /  ^li^/'~\^'l^r--^  V~~~  Dorsal  column 

Visceral  motor  column 

,,  _  _  '  Lateral  column 

Somatic  motor  column    .  ,  _     _ 

Ventral  column 


Fig.  66. — Diagrammatic  transverse  section  through  the  spinal  cord  of  a 
fish  (Menidia)  to  illustrate  the  relations  of  the  functional  columns  of  the 
gray  matter  to  the  nerve  roots.  The  relations  of  the  visceral  sensory 
component  are  problematical,  and  fibers  of  the  visceral  motor  component 
probably  emerge  with  the  dorsal  root,  as  well  as  with  the  ventral  root, 
though  only  the  latter  are  included  in  the  diagram. 

however,  their  components  are  rearranged  in  longitudinal  col- 
umns which  cut  across  and  obscure  the  primary  segmentation. 
The  sensory  root-fibers  and  their  terminal  gray  centers  occupy 
the  dorsal  part  of  the  spinal  cord  and  the  motor  roots  and  their 
centers  the  ventral  part  (Figs.  66  and  67).  In  the  brain  the 
same  arrangement  prevails,  the  sensory  centers  lying  dorsal  to 
the  motor.  In  the  cranial  nerves,  moreover,  the  four  primary 
groups  of  functional  systems  of  the  peripheral  nerves  are  more 
clearly  differentiated  than  in  the  spinal  nerves,  and  from  this 


THE  MEDULLA  OBLONGATA  AND  CEREBELLUM     151 

it  follows  that  their  primary  centers  are  correspondingly  highly 
developed  and  distinct.  The  medulla  oblongata,  in  fact,  is 
divided  into  four  longitudinal  columns  related  respectively  to 
the  great  primary  groups  of  functional  systems.  In  fishes, 
where  the  amount  of  correlation  tissue  is  less  than  in  man,  these 
four  primary  columns  appear  as  well-defined  ridges  in  the  wall 
of  the  fourth  ventricle. 

An  enlarged  view  of  the  medulla  oblongata  of  the  sturgeon, 
which  is  very  similar  to  that  of  the  dogfish,  is  seen  in  Fig.  68, 
which  also  illustrates  the  arrangements  of  the  primary  sensory 
and  motor  centers  in  cross-section  at  several  different  levels. 


Somatic  sensory  column 

Visceral  sensory  column 

Visceral  motor  column 

Somatic  motor  column 


Fig.  67.— Diagrammatic  transverse  section  through  the  human  spinal 
cord.  Compare  Figs.  56  to  59  and  note  the  relatively  greater  size  of  the 
dorsal  gray  columns  and  dorsal  funiculi  in  man  than  in  the  fish  (Fig.  66). 
This  is  correlated  with  the  greater  importance  in  man  of  the  ascending 
connections  between  the  cord  and  the  brain  (see  p.  129). 

Figure  69  shows  a  cross-section  through  the  medulla  oblongata 
in  the  region  of  the  vagus  nerve  in  another  fish,  the  sea-robin. 
In  all  of  these  cases  the  four  principal  functional  s^^stems  (see 
pp.  76  and  79-94)  are  arranged  in  longitudinal  columns  from 
the  dorsal  to  the  ventral  surface  in  the  order:  somatic  sensory, 
visceral  sensory,  visceral  motor,  and  somatic  motor  centers,  as 
indicated  diagrammatically  on  the  left  side  of  Fig.  69.  The 
arrangement  of  the  peripheral  nerve-fibers  of  these  systems  is 
indicated  on  the  right  side.  Figure  70  illustrates  a  cross-section 
through  the  corresponding  region  of  the  medulla  oblongata  in  an 
early  human  embryo,  where  the  same  general  arrangement  of 
the  sensori-motor  centers  is  evident. 


152 


INTRODUCTION  TO   NEUEOLOGY 


Cerebellum 


N.  1.  1.  VII 

Lobus  lineae  lateralis  "• 

f 

VIII    ' 


N   1   1 


Tuberculum 
acusticum 


Fasc.  long,  med 
Lobus  visceralis 


IX 


Fig.  68. — The  medulla  oblongata  and  cerebellum  of  the  lake  sturgeon 
(Acipenser  rubicundus)  to  show  the  longitudinal  columns  which  have  been 
differentiated  in  correlation  with  the  peripheral  functional  systems.  Com- 
pare Figs.  43  and  44  and  note  that  the  " Lobus  linese  lateraUs "  and  "Tu- 
berculum acusticmn"  of  this  figure  together  correspond  to  the  "acoustico- 
lateral  area"  of  the  dogfish.  A  is  a  dorsal  view  with  the  membranous  roof 
of  the  fourth  ventricle  removed  to  show  the  longitudinal  columns  within 
the  ventricle.  B,  C,  and  D  are  sketches  of  cross-sections  at  the  levels 
indicated  in  which  the  four  functional  columns  are  diagrammatically  shaded, 
the  somatic  motor  by  white  circles,  the  visceral  motor  by  white  rectangles, 
the  visceral  sensory  by  obhque  cross-hatching,  and  the  somatic  sensory  by 
vertical  cross-hatching.  The  Roman  numerals  refer  to  the  cranial  nerves. 
(From  Johnston's  Nervous  System  of  Vertebrates.) 


THE  MEDULLA  OBLONGATA  AND  CEREBELLUM 


153 


Figure  71  gives  a  view  of  the  adult  human  medulla  oblongata 
and  midbrain  after  the  removal  of  the  cerebellum  and  mem- 


Somatic  sensory  column 
Visceral  sensory  column 

Visceral  motor  column 
Somatic  motor  column 


Acoustic  area 
Spinal  V  tract 
Vagal  lobe 

Nucleus  ambiguus 
Cutaneous  root  X 
Visceral  sensory  root  X 
Visceral  motor  root  X 
Reticular  formation 
Ventral  column 

Spinal  nerve  (XII) 


Fig.  69. — Diagrammatic  cross-section  through  the  medulla  oblongata 
at  the  level  of  the  vagus  nerve  in  a  bony  fish  (the  sea-robin,  Prionotus  caro- 
Unus),  to  illustrate  the  arrangement  of  the  four  principal  functional  columns. 

branous  roof  of  the  fourth  ventricle.  (For  the  form  of  the  ob- 
longata, as  seen  from  the  side  and  from  below,  see  Figs.  45  and 
53.)     In  this  figure  the  positions  of  the  primary  sensory  and 


Roof  plate 
Fourth  ventricle 


Somatic  sensory  column 

Visceral  sensory  column 

Visceral  motor  column 
Somatic  motor  column 


Dorso-lateral  plate 


Limiting  sulcus 


Ventro-lateral  plate 

llfei X  nerve 

XII  nerve 


Floor  plate 

Fig.  70. — Diagrammatic  cross-section  through  the  medulla  oblongata 
at  the  level  of  the  vagus  nerve  of  a  human  embryo  of  10.2  mm.  (fifth  week), 
to  illustrate  the  arrangement  of  the  four  principal  functional  colmnns. 
(Compare  Fig.  69.) 

motor  nuclei  are  drawn  as  projected  upon  the  dorsal  surface, 
the  motor  centers  on  the  left  and  the  sensory  centers  on  the 
right.     The  somatic  motor  nuclei  are  indicated  by  circles,  the 


154 


INTRODUCTION   TO   NEUROLOGY 


general  visceral  motor  nuclei  by  small  dots,  the  special  visceral 
motor  nuclei  by  large  dots,  the  visceral  sensory  nuclei  by  double 


Trigonum 
hypoglossi 
Nuc.  spinalis  V 


Nuo.  com. 
Cajal 


Fig.  71. — Dorsal  view  of  the  human  midbrain  and  medulla  oblongata 
after  the  removal  of  the  cerebellum  and  the  roof  of  the  fourth  ventricle, 
with  the  positions  of  the  cranial  nerve  nuclei  projected  upon  the  surface. 
The  motor  nuclei  are  indicated  on  the  left  side  and  the  sensory  nuclei  on  the 
right.  The  somatic  motor  nuclei  are  indicated  by  circles,  the  general  vis- 
ceral efferent  nuclei  by  small  dots,  and  the  special  visceral  efferent  nuclei  by 
large  dots.  The  general  somatic  sensory  area  is  indicated  by  horizontal  lines, 
the  visceral  sensory  area  by  double  cross-hatching,  and  the  special  somatic 
sensory  area  by  open  stipple.     (Compare  Figs.  77,  86,  and  114.) 

n.IV,  Nervus  trochlearis;  nuc.com.Cajal,  the  commissural  nucleus  of 
Ramon  y  Cajal;  n7/c. 77/  E-W.,  the  small-celled  visceral  motor  nucleus  of  the 
III  nerve,  or  nucleus  of  Edinger-Westphal ;  nuc.III  lat.,  lateral  nucleus  of 
III  nerve;  nuc.  Ill  med.,  medial  nucleus  of  III  nerve;  nuc.  IV,  nucleus  of  IV 
nerve;  nuc.mesenc.V,  mesencephalic  nucleus  of  V  nerve;  nuc.mot.V,  motor 
nucleus  of  V  nerve;  nuc.mot.VII,  chief  motor  nucleus  of  VII  nerve;  nuc.sal. 
inf.,  nucleus  salivatorius  inferior;  nuc.sal.swp.,  nucleus  salivatorius  superior; 
nuc.sensor.V,  chief  sensory  nucleus  of  V  nerve;  nuc.VI,  nucleus  of  VI  nerve; 
nuc.  XII,  nucleus  of  XII  nerve;  n.V,  nervus  trigeminus. 


THE  MEDULLA  OBLONGATA  AND  CEREBELLUM 


155 


cross-hatching,  the  general  somatic  sensory  nuclei  by  single 
cross-hatching,  and  the  cochlear  and  vestibular  nuclei  (special 
somatic  sensory)  by  open  stipple  bounded  by  heavy  lines. 

Figure  72  illustrates  the  appearance  of  a  cross-section  through 
the  adult  human  medulla  oblongata  at  the  level  of  the  roots  of 
the  IX  nerve,  and  Fig.  73  presents  an  analysis  of  a  section 
slightly  nearer  the  spinal  cord  at  the  level  of  the  X  nerve.  Fig- 
ure 74  is  a  diagrammatic  representation  of  the  relations  of  the 


Vagoglossopharyngeal 

roots    Nucleus  of  the 
Restiform    1    fasciculus  solitarius 
boay        I  I  Tiema 


Vagus  nucleus 

Fasciculus  sohtarius 

De  cending  root  of  vestibu- 
lar nerve  (VIII) 
Vafeo  glossophar- 
yngeal roots 


Fasc.  long, 
medialis 
Nuc  spinal  V. 
\       tract 
Spinal  V.  tr. 
N  ambiguus 
Ohvo  cereb.  tract 
orbal  acces.  olive 


ternal  arcuate  fibers 
Medial  lemniscus 

Medial  acces.  olive 


Inferior  olive 


Pyramid 
External  arcuate  fibers 


Fig.  72. — Cross-section  through  the  adult  human  medulla  oblongata  at  the 
level  of  the  IX  cranial  nerve.     (From  Cunningham's  Anatomy.) 


four  principal  functional  systems  at  the  same  level  as  shown  by 
Fig.  73  for  comparison  with  Figs.  66,  67,  69,  70.  It  is  obvious 
that,  while  the  general  relations  in  the  human  embryo  (Fig.  70) 
resemble  tolerably  closely  those  of  the  adult  fish  (Fig.  69),  in  a 
human  adult  (Fig.  74)  this  primary  arrangement  has  been 
greatly  disturbed  by  the  addition  of  many  new  tracts  and  cen- 
ters in  the  ventral  part  of  the  cross-section. 


156 


INTRODUCTION   TO    NEUROLOGY 


We  cannot  here  undertake  an  analysis  of  the  complex  reflex 
connections  of  the  medulla  oblongata.     In  general,  each  of  the 


Nuc.  dorsalis  vagi 

Niic.  fasc.  solitarius, 

Faso.  solitarius. 


Ala  cinerea 
Trigonmn  hypoglossi 
Nuc.  vestibularis  spinalis 

Fasc.  long.  med. 

Lemniscus  V 


Inferior  olive 
XII  root 


Fig.  73. — Diagrammatic  cross-section  through  the  human  medulla 
oblongata  at  the  level  of  the  vagus  nerve,  illustrating  details  of  functional 
localization  in  addition  to  those  shown  in  Fig.  72. 


Vise.  mot.  col 
Som.  mot.  col 


Area  aoustica 
Nuc.  fasc.  sol. 
Nuc.  dors.  X 
Fasc.  solitarius 
Cor.  restiforme 
Spinal  V  tract 

Cutan.  root  X 
Vise.  sens,  root  X 
Vise.  mot.  root  X 
Nuc.  ambiguus 
Reticular  form. 
Inferior  olive 
XII  root 


Fig.  74. — Diagrammatic  cross-section  through  the  adult  human  medulla 
oblongata  at  the  same  level  as  shown  in  Fig.  73,  for  comparison  of  the 
arrangement  of  the  principal  functional  columns  with  that  of  Figs.  69 
and  70. 

primary  terminal  nuclei  of  the  sensory  roots  of  the  cranial  nerves 
effects  four  types  of  connections:  (1)  direct  reflex  connections 


THE  MEDULLA  OBLONGATA  AND  CEREBELLUM     157 

with  the  motor  nuclei  of  the  medulla  oblongata,  these  connec- 
tions being  effected  through  the  reticular  formation  (Figs.  69, 
73) ;  (2)  descending  reflex  connections  with  the  motor  centers  of 
the  spinal  cord,  by  way  of  the  bulbo-spinal  tracts  (such  as  the 
vestibulo-spinal  tract,  Fig.  59);  (3)  connections  with  the  cere- 
bellum (this  applies  only  to  such  functional  sj^stems  as  have  pro- 
prioceptive value,  of  which  the  vestibular  nerve  from  the  semi- 
circular canals  of  the  ear  is  the  most  important) ;  (4)  connections 
with  the  thalamus  and  (after  a  synapse  here)  with  the  cerebral 
cortex. 

The  fibers  of  the  type  last  mentioned  comprise  the  bulbar 
lemniscus  (Figs.  64,  77) ;  of  this  there  are  several  distinct  parts, 
two  of  which  require  special  mention,  viz.,  the  trigeminal  lem- 
niscus and  the  lateral  lemniscus.  The  skin  of  the  head  is  inner- 
vated chiefly  by  the  trigeminal  nerve  (V  pair)  and  the  fibers  of 
this  type  terminate  in  the  general  somatic  sensory  area  (known  as 
the  chief  sensory  V  nucleus  and  the  spinal  V  nucleus  or  gelatinous 
substance  of  Rolando,  Figs.  71-74).  After  a  synapse  in  this 
area  the  fibers  of  the  trigeminal  lemniscus  cross  to  the  opposite 
side  and  ascend  to  the  thalamus  in  a  pathway  distinct  from  all 
other  lemniscus  fibers  (see  p.  180  and  Figs.  64,  75,  77,  78,  81). 

The  lateral  or  acoustic  lemniscus  comprises  by  far  the  largest 
component  of  the  bulbar  lemniscus  complex.  Its  fibers  arise 
from  the  terminal  nuclei  of  the  cochlear  nerve  (VIII  pair.  Fig. 
71)-,  cross  at  once  to  the  opposite  side  of  the  brain,  and  ascend 
to  the  midbrain  (Fig.  75).  Some  of  these  fibers  continue  di- 
rectly to  the  thalamus,  where  they  end  in  the  medial  geniculate 
body  (Fig.  77);  others  terminate  in  the  roof  of  the  inferior 
colliculus  of  the  midbrain.  After  a  synapse  here  and  various 
reflex  connections,  the  nervous  impulse  may  be  carried  forward 
to  the  medial  geniculate  body  of  the  thalamus  by  way  of  the 
brachium  quadrigeminum  inferius  (Figs.  75,  86).  (Regarding 
this  system  see  further  on  pp.  195^203.) 

In  fishes  there  is  an  ascending  secondary  visceral  and  gusta- 
tory tract,  or  visceral  lemniscus,  from  the  visceral  sensory  area  to 
the  midbrain  (p.  246) ;  this  tract  no  doubt  occurs  in  the  human 
brain  also,  though  its  exact  course  has  never  been  demonstrated. 

Having  now  reviewed  cursorily  the  primary  sensory  and  motor 
centers  of  the  medulla  oblongata,  we  must  next  examine  some  of 


158  INTRODUCTION  TO  NEUROLOGY 

the  centers  of  correlation.  As  has  already  been  indicated,  all  of 
these  centers  are  interconnected  by  correlation  neurons  similar 
to  those  of  the  spinal  cord  (Figs.  60,  61).  These  neurons  are 
loosely  arranged  in  the  spaces  between  the  sensory  and  motor 
groups  of  nuclei,  this  tissue  being  termed  the  reticular  formation 
(this  region  is  also  called  the  tegmentum,  see  pp.  65,  127  and 
Figs.  69,  74).  But  the  chief  centers  of  correlation  of  the  brain 
stem  are  found  in  specially  enlarged  nuclei  of  the  midbrain  and 
thalamus,  some  of  which  are  mentioned  in  the  next  chapter. 

In  its  more  ventral  parts  the  medulla  oblongata  contains  a 
number  of  large  correlation  centers  and  important  conduction 
pathways  between  remote  parts  of  the  brain.  Of  the  former,  the 
largest  are  the  inferior  olives  (Figs.  72,  73,  74),  deeply  buried 
masses  of  gray  matter  arranged  in  the  form  of  a  hollow  shell  of 
complex  shape  on  each  side  of  the  median  plane.  The  olives 
receive  fibers  from  the  thalamus  and  spinal  cord  and  discharge 
into  the  cerebellum  (olivo-cerebellar  fibers  of  Fig.  72).  Their 
functions  are  unknown. 

The  cerebellum  has  already  been  referred  to  as  a  great  supra- 
segmental  mechanism  of  unconscious  motor  coordination.  It 
is  connected  with  the  underlying  brain  stem  by  three  pairs  of 
stalks  or  peduncles,  two  of  which  join  the  medulla  oblongata  and 
one  the  midbrain.  The  inferior  peduncle  (restiform  body) 
connects  with  the  dorsal  margin  of  the  medulla  oblongata  and 
carries  fibers  into  the  cerebellum  from  the  spinal  cord  and  ob- 
longata. The  middle  peduncle  (brachium  pontis)  connects 
with  the  pons  and  most  of  its  fibers  convey  impulses  from  the 
nuclei  of  the  pons  to  the  cerebellum.  The  superior  peduncle 
(brachium  conjunctivum)  connects  with  the  cerebral  peduncle 
in  the  floor  of  the  midbrain  and  contains  chiefly  fibers  which 
descend  from  the  cerebellum,  cross  the  midplane  under  the 
aqueduct  of  Sylvius,  and  terminate  in  or  near  the  red  nucleus 
(Fig.  75,  nucleus  ruber).  The  internal  structure  and  connec- 
tions of  the  cerebellum  will  be  further  considered  on  page  186. 

Summary. — The  rhombencephalon  includes  the  medulla 
oblongata  and  cerebellum,  that  is,  all  parts  of  the  brain  below 
the  isthmus.  All  of  the  cranial  nerves  except  the  first  four  pairs 
connect  with  the  medulla  oblongata.  An  analysis  of  the  func- 
tional components  of  the  cranial  nerves  shows  that  they  can 


THE  MEDULLA  OBLONGATA  AND  CEREBELLUM     159 

best  be  understood  by  considering  each  functional  system  of 
fibers  as  a  unit  and  studying  the  connections  of  each  component 
separately.  These  connections  are  summarized  in  a  table  on  pp. 
146,  147.  The  medulla  oblongata  of  lower  vertebrates  and  of 
the  human  embryo  is  seen  to  be  composed  chiefly  of  the  primary 
centers  related  to  these  functional  components  of  the  peripheral 
nerves,  arranged  in  longitudinal  columns  in  the  order  from  dorsal 
to  ventral  surfaces  on  each  side  of  somatic  sensory,  visceral 
sensory,  visceral  motor,  somatic  motor  centers.  The  same 
arrangement  appears  in  the  adult  human  oblongata,  though 
somewhat  distorted  by  the  presence  of  large  masses  of  correla- 
tion tissue  and  of  large  conduction  tracts  which  are  not  present 
in  the  lower  vertebrates.  The  sensory  centers  of  the  oblongata 
are  connected  locally  with  the  adjacent  motor  centers  and  also 
by  longer  tracts  with  the  spinal  cord,  cerebellum,  and  thalamus. 
The  latter  fibers  constitute  the  bulbar  lemniscus,  of  which  several 
functional  components  can  be  distinguished,  the  most  important 
being  the  trigeminal  lemniscus  for  general  cutaneous  sensibility 
and  the  lateral  or  acoustic  lemniscus  for  auditory  sensibility. 
The  cerebellum  is  a  proprioceptive  center  developed  out  of  the 
vestibular  area  of  the  medulla  oblongata. 

Literature 

The  details  of  the  structure  and  fxuictions  of  the  parts  mentioned  in  this 
and  the  following  chapters  will  be  found  fully  presented  in  the  standard  text- 
books of  human  anatomy  and  physiology  and  in  the  medical  text-books  of 
neurology,  and  all  of  this  literature  up  to  the  year  1899  is  summarized  in 
Barker's  Nervous  System  and  Its  Constituent  Neurones.  See  also  W. 
von  Bechterew,  Die  Funktionen  der  Nervencentra,  Jena,  1908  to  1911, 
3  vols.  For  discussions  of  comparative  neurology  and  the  evolution  of  the 
nervous  system,  reference  may  be  made  to  articles  in  the  neurological 
journals,  especially  the  Journal  of  Comparative  Neurology;  see  also  the 
Bibliographies  on  pp.  36,  124,  193,  and  223,  and  the  following  works: 

Herrick,  C.  Judson.  1899.  The  Cranial  and  First  Spinal  Nerves  of 
Menidia:  A  Contribution  Upon  the  Nerve  Components  of  the  Bony  Fishes, 
Jour.  Comp.  Neurology,  vol.  ix.,  pp.  153-455. 

— .  1913.  Brain  Anatomy,  Wood's  Reference  Handbook  of  the  Medical 
Sciences,  3d  ed.,  vol.  ii,  pp.  274-342. 

— .  1914.  Cranial  Nerves,  ibid.,  vol.  iii,  pp.  321-339. 

Johnston,  J.  B.  1906.  The  Nervous  System  of  Vertebrates,  Philadel- 
phia. 

— .  1909.  The  Central  Nervous  System  of  Vertebrates,  Spengel  s 
Ergebnisse  und  Fortschritto  der  Zoologie,  Bd.  2.  Heft  2,  Jena. 

Edinger,  L.  1908.  Vorlesungen  iiber  den  Ban  der  nervosen  Zentral- 
organe,  7th  Auflage,  Band  2,  Vergleichcnde  Anatomic  des  Geliii'ns,  Leipzig. 

— .  1911.  Idem,  8th  Auflage,  Band  1. 


CHAPTER  X 

THE    CEREBRUM 

The  cerebrum  includes  all  of  the  brain  lying  in  front  of  the 
isthmus,  that  is,  the  midbrain  (mesencephalon),  betweenbrain 
(diencephalon),  and  cerebral  hemispheres  (telencephalon),  the 
two  last  comprising  the  forebrain  (prosencephalon).  It  con- 
tains the  primary  sensory  centers  of  the  olfactory  nerves  (I 
pair),  the  sensory  correlation  centers  of  smell  and  sight,  the 
primary  motor  and  sensory  centers  of  the  oculomotor  and  troch- 
lear nerves  (III  and  IV  pairs)  for  movements  of  the  eyes,  and  all 
of  the  most  important  higher  correlation  centers  of  the  brain. 
These  higher  correlation  centers  make  up  by  far  the  larger  part 
of  its  substance  in  the  human  brain,  though  in  fishes  the  converse 
relation  prevails,  with  the  primary  sensori-motor  centers  and  the 
simpler  correlation  mechanisms  making  up  the  larger  part  (see 
Figs.  43,  44,  pp.  Ill,  112). 

The  mesencephalon  (midbrain)  is  that  part  of  the  brain  in 
which  the  early  embryonic  neural  tube  (Figs.  46-51,  pp.  116- 
119)  has  been  least  modified  in  the  adult.  The  ventral  part 
of  the  midbrain,  ^.  e.,  the  part  lying  ventrally  of  the  ventricle, 
which  is  here  termed  the  aqueduct  of  Sylvius,  is  called  the  cere- 
bral peduncle;  the  dorsal  part  is  the  corpora  quadrigemina,  the 
upper  pair  of  these  four  eminences  being  the  superior  colliculi, 
and  the  lower  pair  the  inferior  colliculi  (see  Fig.  71,  p.  154). 

The  corpora  quadrigemina  contain  important  correlation 
centers,  the  superior  colliculus  chiefly  visual  (p.  209)  and  the 
inferior  colliculus  chiefly  auditory  (p.  202).  The  cerebral 
peduncle,  as  the  name  implies,  contains  the  great  ascending  and 
descending  fiber  tracts  between  the  forebrain  above  and  the 
medulla  oblongata,  cerebellum,  and  spinal  cord  below.  The 
arrangement  of  some  of  these  tracts  can  be  seen  in  Fig.  75.  The 
cerebral  peduncle  also  contains  the  nuclei  of  origin  for  the  motor 
fibers  of  the  III  and  IV  pairs  of  cranial  nerves  and  several  masses 
160 


THE    CEREBRUM 


161 


of  gray  matter  devoted  to  motor  coordination,  such  as  the  black 
substance  (substantia  nigra)  and  the  red  nucleus  (nucleus  ruber, 
see  p.  189). 

The  diencephalon  (betweenbrain  or  thalamencephalon)  in 
early  embryonic  development  is  a  transverse  region  of  the  simple 
neural  tube  (Fig.  48,  p.  117)  surrounding  the  third  ventricle.     In 

Tectum  mesencephali 
Commissura  tecti 
Nuc.  and  tr.  mesen.  V 

Tractus  opticas ^     /^#        /\  \;\^><^:>^  ^Tr.  spino-tectaUs 

//n  i/l-Jl        fh&i  •mL-^'^''^  tv^^C    ^Tr.  thalamo-olivaria 

rii^t^ri_#^  n        ^  W        ^X^Trigeminallemn.cu. 

'~"  Lateral  and  spinal 


Vent,  tegm 

decuss. 
Tr.  rubro-' 

spinalis 
Tr.  cortico- 

bulb.  lat.' 
Tr.   man 

pedunc 


Tr.  cortico- 
bulb,  med 


Fig.  75. — ^Diagrammatic  cross-section  through  the  midbrain  at  the  level 
of  the  superior  colliculus  (cf.  Fig.  71),  to  illustrate  the  arrangement  of  the 
chief  conduction  pathways:  Aq.,  Aqueduct  of  Sylvius;  m.,  medial  part  of 
motor  nucleus  of  oculomotor  nerve;  n.III,  oculomotor  nerve;  tiuc.III, 
motor  nucleus  of  oculomotor  nerve;  Tr. mam. -pedunc,  tractus  mamillo- 
peduncularis.  The  fibers  of  the  dorsal  tegmental  decussation  {Dors, 
tegm.decuss.,  also  known  as  the  fountain  decussation  of  Meynert)  arise 
from  the  roof  of  the  midbrain  (tectum  opticum)  and  immediately  after 
crossing  the  median  plane  descend  toward  the  spinal  cord,  where  they  form 
part  of  the  tractus  tecto-spinalis  (Fig.  59,  p.  130).  The  fibers  of  the  ventral 
tegmental  decussation  {Vent. tegm.decuss.,  also  known  as  Forel's  decussa- 
tion) in  a  similar  way  arise  from  the  nucleus  ruber  and  enter  the  opposite 
tractus  rubro-spinalis. 


the  adult  human  brain,  however,  it  is  entirely  concealed  b}'  other 
parts.  The  posterior  part  of  it  is  visible  from  the  side  in  the 
dissection  shown  in  Fig.  45  (p.  114),  its  medial  surface  in  Fig. 
52  (p.  119),  and  its  dorsal  surface  is  exposed  in  the  dissection, 
Fig.  76  (see  also  Fig.  77).  This  part  of  the  brain  is  devoted 
11 


162 


INTRODUCTION   TO    NEUROLOGY 


wholly  to  various  types  of  correlation.  It  has  three  main  divi- 
sions, the  thalamus,  the  epithalamus,  and  the  hypothalamus,  of 
which  the  two  last  are  dominated  by  the  olfactory  apparatus 
(see  p.  220). 

The  epithalamus  consists  of  the  membranous  chorioid  plexus 
which  forms  the  roof  of  the  third  ventricle  (Fig.  79),  the  pineal 
body  or  epiphysis  (Fig.  76),  the  habenula  (marked  trigonum 


G«nu  of  corpus  callosum 
Corpus  callosum  (cut) 

Cavum  septi  pellucidi 
Septum  pellucid  um 

Caudate  nucleus 

Fornix 

Foramen  interventriculare 
Anterior  commissure 
Ant.  tubercle  of  thalamus 
— Massa  intermedia 

Third  ventricle 
Stria  terminalis 
Taenia  thalami 
Trigonum  habenulae 
Posterior  commissure 
Stalk  of  pineal  body 
Pulvinar 
=S~~~^Pineal  body 


Non-ventricular  part  of- 
thalamus 

Groove  corresponding. 

to  fornix 
Quadrigeminal  bodies- 

Trochlear  nerve- 

Brachium  pontis- 

Brachium  conjunctivum 

Lingula 


Medulla  oblongata 


Fig.  76. — A  dissection  of  the  brain  from  above  to  expose  the  thalamus  and 
corpus  striatum.     (From  Cunningham's  Anatomy). 


habenulae  on  Fig.  76),  and  the  stria  medullaris,  a  fiber  tract  which 
connects  the  olfactory  centers  of  the  cerebral  hemispheres  with 
the  habenula  (Figs.  78,  79).  The  habenula  is  a  center  for  the  cor- 
relation of  olfactory  sensory  impulses  with  the  various  somatic 
sensory  centers  of  the  dorsal  part  of  the  thalamus.  The  pineal 
body  of  some  lower  vertebrates  is  a  sense  organ,  apparently 
visual  in  function  and  known  as  the  parietal  eye  (p.  212);  in 


THE    CEREBRUM  163 

man  its  primary  sensory  function  is  lost  and  it  is  said  to  pro- 
duce an  important  internal  secretion  whose  physiological  value 
is  still  obscure. 

The  hypothalamus  includes  the  tuber  cinereum  and  mammil- 
lary  bodies  (see  Figs.  53,  78,  and  79),  these  structures  being 
olfactory  centers,  and  the  hypophysis  or  pituitary  body  (which 
has  been  removed  from  the  specimen  shown  in  Fig.  53,  its  point 
of  attachment  being  the  infundibulum).  The  hypophysis  is  a 
glandular  organ  which  produces  an  internal  secretion  of  great 
importance  in  maintaining  the  proper  balance  of  the  metabolic 
activities  of  the  body.  The  hypothalamus  is  an  important  cen- 
ter for  the  correlation  of  olfactory  impulses  with  various  visceral 
functions,  including  probably  the  sense  of  taste. 

The  thalamus  is  in  the  human  brain  chiefly  a  sort  of  vestibule 
through  which  the  systems  of  somatic  sensory  nervous  impulses 
reach  the  cerebral  cortex.  There  are,  however,  two  parts  of  the 
thalamus  which  should  be  clearly  distinguished.  The  ventral 
part  contains  chiefly  motor  coordination  centers.  It  is  feebly 
developed  in  the  human  brain,  where  it  is  termed  the  subthala- 
mus  (not  to  be  confused,  as  is  often  done,  with  the  hypothala- 
mus, see  Figs.  78,  79,  and  81).  The  dorsal  part  of  the  thalamus, 
in  its  turn,  contains  two  distinct  types  of  sensory  correlation 
centers:  (1)  primitive  sensory  reflex  centers,  chiefly  in  the  medial 
group  of  thalamic  nuclei ;  (2)  the  more  lateral  nuclei  which  form 
the  cortical  vestibule  to  which  reference  was  made  above. 
These  lateral  nuclei  are  sometimes  called  the  new  thalamus 
(neothalamus)  in  distinction  from  all  of  the  other  thalamic 
nuclei  which  form  the  old  thalamus  (palseothalamus) . 

The  centers  which  comprise  the  new  thalamus  make  up  by  far 
the  larger  part  of  the  thalamus  in  the  human  brain  and  include 
the  following  nuclei:  the  lateral,  ventral,  and  posterior  nuclei 
(for  general  cutaneous  and  deep  sensibility)  receiving  the 
spinal,  trigeminal,  and  medial  lemnisci;  the  lateral  geniculate 
body  and  pulvinar  (visual  sensibility)  receiving  the  optic  tracts; 
the  medial  geniculate  body  (auditory  sensibility)  receiving  the 
lateral  or  acoustic  lemniscus.  The  lateral  and  medial  genicu- 
late bodies  comprise  the  metathalamus  of  the  B.  N.  A.  (see  p. 
121  and  Fig.  50,  p.  118),  which  in  this  work  are  described  as 
part  of  the  thalamus. 


^^ornix 


Lemnis.  spinalis 

Lemnis.  medialis 

Lemnis.  lateralis 

Lemniscus  V 


Superior  olive 


Ala  cinerea 


Nuclei  of  funiculi  gracilis 
and  cuneatus 


Fasciculus  solitarius 

Nuc.  commissuralis  of  Cajal 


Nucleus  spinalis  V 


Fig.  77. — A  diagram  of  the  human  brain  stem  from  above  after  the  re- 
moval of  the  cerebral  hemisphere,  to  illustrate  the  nuclei  of  the  thalamus 
and  some  of  the  chief  fiber  tracts  connected  with  them.  Compare  Figs.  71 
and  45.  The  fibers  of  the  sensory  radiations  between  the  thalamus  and  the 
cerebral  cortex  fall  into  three  groups :  somesthetic  (som.)  for  touch,  tempera- 
ture, and  spatial  discrimination,  auditory  (au.),  and  optic  (opt.).  Descend- 
ing cortico-thalamic  fibers  are  shown  in  connection  with  the  somesthetic 
radiation  only ;  but  such  fibers  are  present  in  the  auditory  and  optic  radia- 
tions also,  ant.,  Anterior  nucleus  of  thalamus;  ep.,  pineal  body  (epiphy- 
sis); c.g.l.,  corpus  geniculatum  laterale;  c.g.m.,  corpus  geniculatum  mediale; 
col.  inf.,  colliculus  inferior;  col.  sup.,  colliculus  superior;  lat.,  lateral  nucleus 
of  thalamus;  med.,  medial  nucleus  of  thalamus;  post.,  posterior  nucleus  of 
thalamus;  pulv.,  pulvinar;  ventr.,  ventral  nucleus  of  thalamus. 
164 


THE    CEREBRUM 


165 


All  of  the  thalamic  nuclei  of  the  lateral  group  (the  neothala- 
mus) are  connected  by  important  systems  of  fibers  with  the 
cerebral  cortex,  these  fibers  running  both  to  and  from  the  cortex 
(Fig.  77).  These  are  called  sensory  projection  fibers  and  all 
pass  through  or  near  the  internal  capsule  of  the  corpus  striatum 
(p.  169).  As  we  have  just  seen,  the  nuclei  of  the  lateral  group 
receive  special  systems  of  somatic  sensory  fibers — optic,  acous- 
tic, and  the  general  cutaneous  and  deep  sensibility  complex  of 

Corpus  callosum^ 
Fimbria!. 
Nucleus  anterior 
Tr.  mamillo-thalamicuss^    s^ 
Nucleus  lateralis^  ^     "^ 
Metathalamus 


Habenula-  —^ 
Fasc.  ret.- 
Nuc.  post.. 
Nuc.  ven.. 

Subthal ^' 

Nuc.  ruber 

Lemn.  V 

Br.  conj ___ 

S.  nigra .— - 

Lemn.  med. 

Tr.  th.-ped. 


Fig.  78. — Diagram  of  the  nuclei  of  the  diencephalon  and  some  of  their 
functional  connections  as  seen  in  parasagittal  section  taken  close  to  the 
median  plane.  The  epithalamus  and  the  hypothalamus  are  stippled. 
Br.conj.,  Brachium  conjunctivum;  Fasc.ret.,  fasciculus  retroflexus;  Lemv. 
med.,  lemniscus  mediaUs;  Lemn.V.,  lemniscus  trigemini;  Nucpost.,  nucleus 
posterior  thalami;  Nuc.ven.,  nucleus  ventralis  thalami;  Svbthal.,  subthala- 
mus;  S.nigra,  substantia  nigra;  Tr.th.-ped.,  tractus  thalamo-peduncularis. 

the  spinal,  trigeminal,  and  medial  Icmnisci.  The  elements  of 
the  latter  complex  (comprising  touch,  temperature,  pain,  general 
proprioceptive  sensibility,  spatial  locahzation,  etc.,  termed  as  a 
whole  the  somesthetic  group)  are  no  doubt  separately  represented 
in  the  thalamus,  but  the  analysis  of  their  respective  thalamic 
centers  has  not  yet  been  completely  effected.  Each  of  the  chief 
functional  regions  of  the  neothalamus  which  have  just  been 
enumerated  is  connected  by  its  own  system  of  projection  fibers 


166 


INTRODUCTION   TO   NEUROLOGY 


with  a  specific  region  in  the  cerebral  cortex,  viz.,  the  optic, 
auditory,  and  somesthetic  projection  centers  (see  p.  273). 
These  tracts  are  known  as  the  optic,  auditory,  and  somesthetic 
radiations  (see  Fig.  80). 

The  old  thalamus  (palsBothalamus)  comprises  the  more 
medial  thalamic  centers  which  were  differentiated  for  the 
primitive  thalamic  correlations  which  are  present  in  fishes  and 
other  lower  vertebrates  which  lack  the  cerebral  cortex.     Clinical 


Corona  radiata 
Caudate  nucleus 


Lateral  (Sylvian) 

fissure 
Internal  capsule 

Island  of  Reil 
Lentiform  nucleus 

External  capsule 


Corpus  callosum 

Fornix 

Chorioid  plexus 

Stria  meduUaris 

Nuc.  ant.  thai. 

Nuc.  medial,  thai. 

Nuc.  lateral,  thai. 

Nuc.  ventral,  thai. 

Subthalamus 

Mammillary  body 

Optic  tract 

Amygdala. 

Lateral  ventricl 

Fig.  79. — Cross-section  through  the  human  cerebral  hemisphere  and 
thalamus,  including  the  mammillary  body  and  the  posterior  end  of  the  an- 
terior nucleus  of  the  thalamus  (cf.  Fig.  78).  At  this  level  the  epithalamus 
is  represented  only  by  the  stria  medullaris  and  the  chorioid  plexus  of  the 
third  ventricle,  the  hypothalamus  by  the  mammillary  body.  The  old 
thalamus  (paleeothalamus)  is  represented  by  the  anterior  and  medial  nuclei 
and  the  subthalamus,  the  new  thalamus  (neothalamus)  by  the  lateral  and 
ventral  nuclei. 

evidence  (see  especially  Head  and  Holmes,  1911)  seems  to  show 
that  many  of  these  primitive  functions  are  retained  in  the  old 
thalamus  in  man,  and  that  some  of  the  conscious  activities  are 
served  by  these  thalamic  centers.  In  other  words,  the  activity 
of  the  cerebral  cortex  is  not  essential  for  all  conscious  processes,, 
though  its  participation  is  necessary  for  others,  particularly 
all  intellectual  and  voluntary  activities.  The  thalamus,  on  the 
other  hand,  can  act  independently  of  the  cortex  in  the  case  of 


THE    CEREBRUM  167 

painful  sensibility  and  the  entire  series  of  pleasurable  and  pain- 
ful qualities;  for  the  thalamic  centers  when  isolated  from  their 
cortical  connections  are  found  to  be  concerned  mainly  with 
affective  experience,  and  destructive  lesions  which  involve  the 
cortex  alone  do  not  disturb  the  painful  and  affective  qualities  of 
sensation  (see  p.  253). 

The  relations  of  the  thalamic  nuclei  and  of  some  of  the  tracts 
connected  with  them  are  shown  as  seen  from  above  in  Fig.  77 
and  in  a  section  parallel  with  the  median  plane  in  Fig.  78. 

The     DlBNCEPHALON 

I.  Epithalamus. 

1 .  Chorioid  plexus  of  the  third  ventricle. 

2.  Pineal  body  (epiphysis). 

3.  Habenula  (receives  the  stria  medullaris  from  the  olfactory  centers 

and  sends  fibers  to  the  cerebral  peduncle). 

II.  Thalamus. 

1.  Dorsal  part. 

(1)  Medial  group  of  nuclei. 

(a)  Medial  nucleus  (receives  fibers  from  the  olfactory  area 
and  neothalamus  and  from  the  trigeminal  lemniscus ; 
sends  fibers  to  the  olfactory  area,  corpus  striatimi, 
subthalamus,  and  probably  cerebral  cortex). 

(6)  Anterior  (or  dorsal)  nucleus  (receives  fibers  from  the 
mammiUary  body  and  sends  fibers  to  the  corpus  stri- 
atum). 

(2)  Lateral  group  of  nuclei  (neothalamus). 

(a)  Lateral,  ventral,   and  posterior  nuclei   (receive  the 

medial,  spinal,  and  trigeminal  lemnisci ;  connect  with 
parietal  and  frontal  cortex  by  ascending  and  descend- 
ing somesthetic  projection  fibers). 

(b)  Pulvinar  and  lateral  geniculate  body  (receive  optic 

tracts;  connect  with  occipital  cortex  by  ascending 
and  descending  optic  projection  fibers). 

(c)  Medial  geniculate  body  (receives  the  lateral  or  acoustic 

lemniscus;  connects  with  temporal  cortex  by  ascend- 
ing and  descending  auditory  projection  fibers). 
[The  two  geniculate  bodies  =  metathalamus,  B.  N.  A.] 

2.  Ventral  part,  or  subthalamus   (a  motor  coordination  center  re- 

ceiving fibers  from  the  dorsal  part  of  the  thalamus,  from  the 
corpus  striatum  and  from  the  pyramidal  tract;  sends  fibers  to 
the  pedunculus  cerebri;  comprises  the  body  of  Luj's,  Forel's 
field  H2,  and  some  adjacent  gray  matter;  is  continuous  behind 
with  the  substantia  nigra  of  the  cerebral  peduncle). 

III.  Hypothalamus. 

1.  Tuber  cinereum  (olfacto-visceral  correlation  center). 

2.  MammiUary  body  (receives  fibers  from  the  olfactory  centers ;  sends 

fibers  to  the  cerebral  peduncle  and  nucleus  anterior  thalami). 

3.  Hypophysis. 


168  INTRODUCTION  TO  NEUROLOGY 

Some  of  these  centers  are  seen  in  cross-section  in  Fig.  79.  The 
preceding  analysis  of  the  diencephalon,  which  differs  in  some 
respects  from  that  of  the  B.  N.  A.  (p.  121),  is  summarized  in  the 
accompanying  table  (p.  167),  which  includes  also  a  few  of  the 
more  important  fiber  tracts  connected  with  each  nucleus. 

In  front  of  the  thalamus  lie  the  corpus  striatum  and  olfactory 
centers  (see  Fig.  45,  p.  114),  and  above  these  last  two  is  spread 
the  great  expanse  of  the  cerebral  cortex  or  pallium.  The  corpus 
striatum  consists  of  masses  of  gray  matter  separated  by  sheets 
of  white  matter,  an  arrangement  which  gives  a  striated  appear- 
ance in  section. 

In  studying  the  comparative  anatomy  of  the  cerebral  hemi- 
spheres we  find  the  corpus  striatum  well  developed  in  some  lower 
vertebrates  which  lack  the  cerebral  cortex,  and  very  highly  de- 
veloped in  others,  like  reptiles  and  birds,  where  the  cortex  is 
present,  though  very  small.  In  these  animals  the  corpus  stri- 
atum appears  to  be  a  reflex  center  of  great  importance  and  of 
higher  order  than  the  thalamus;  and  the  dfferentiation  of  this 
apparatus  seems  to  have  been  a  necessary  precursor  of  the  elabo- 
ration of  the  cerebral  cortex  as  we  find  it  in  the  mammals. 

The  functions  of  the  mammalian  corpus  striatum  are  very 
obscure.  It  is  connected  by  both  ascending  and  descending 
fibers  with  various  nuclei  of  the  thalamus  and  cerebral  peduncle, 
and  also  with  the  cerebral  cortex.  Ramon  y  Cajal  is  of  the 
opinion  that  the  mammalian  striatum  functions  chiefly  to  re- 
inforce the  descending  motor  impulses  which  leave  the  cerebral 
cortex,  these  systems  of  fibers  giving  off  collateral  branches  as 
they  traverse  it,  and  the  striatum  itself  sending  important  de- 
scending tracts  into  the  thalamus  and  cerebral  peduncle. 

The  white  matter  of  the  corpus  striatum  consists  partly  of  the 
fibers  already  mentioned  as  passing  between  it  and  the  thalamus 
and  cortex,  but  chiefly  of  fibers  passing  between  the  cortex  and 
deeper  parts  of  the  brain  stem,  having  no  functional  connection 
with  the  striatum  itself.  These  are  called  projection  fibers. 
They  are  partly  ascending  and  descending  fibers  passing  between 
the  thalamus  and  the  cortex  (the  optic,  auditory,  and  somesthetic 
projection  systems,  or  radiations,  which  have  already  been 
mentioned,  p.  165),  and  partly  descending  motor  projection 
fibers  of  the  cortico-spinal  or  pyramidal  tract  (p.  140  and  Fig. 


THE    CEREBRUM  169 

64,  p.  141),  cortico-bulbar  tract,  and  cortico-pontile  tracts  (pp. 

187  and  289). 

The  gray  matter  of  the  corpus  striatum  is  gathered  into  two 
principal  masses,  the  caudate  nucleus  and  the  lentiform  nucleus 
(so-named  from  their  shapes),  and  most  of  the  projection  fibers 
pass  between  these  nuclei  in  a  wide  band  of  white  matter  known 
as  the  internal  capsule.  The  broken  ends  of  the  internal  capsule 
fibers  are  seen  in  the  dissection  shown  in  Fig.  45  (p.  114).  As 
these  fibers  radiate  from  the  internal  capsule  toward  the  cortex 
they  are  called  the  corona  radiata  (Fig.  79).  The  external 
capsule  is  a  thinner  sheet  of  fibers  externally  of  the  lentiform 
nucleus  (Figs.  79  and  80).  Figure  79  illustrates  a  transverse 
section  through  the  cerebral  hemisphere,  showing  the  relations 
of  the  thalamus  and  corpus  striatum. 

The  exact  arrangement  of  the  functional  systems  of  sensory 
and  motor  projection  fibers  within  the  internal  capsule  is  a 
matter  of  great  clinical  importance;  for  a  considerable  propor- 
tion of  apoplexies  and  other  cerebral  diseases  result  from  hemor- 
rhage or  other  injury  of  the  internal  capsule  causing  destruction 
of  some  of  its  fibers.  A  partial  paralysis  will  result,  whose  symp- 
toms will  depend  upon  the  particular  functional  systems  of  pro- 
jection fibers  affected.  Figure  80  illustrates  the  arrangement 
of  some  of  the  systems  of  fibers  of  the  internal  capsule  as  seen 
in  a  horizontal  section  through  the  cerebral  hemispheres. 

The  olfactory  centers  of  the  cerebral  hemispheres  and  the 
cerebral  cortex  will  be  considered  in  chapters  which  follow. 

Summary. — The  cerebrum  contains  the  primary  centers  for 
the  I,  II,  III,  and  IV  pairs  of  cranial  nerves,  but  most  of  its 
substance  is  concerned  with  the  higher  centers  for  the  correla- 
tion of  sensory  impressions,  especially  those  involved  in  the 
psychic  activities.  The  midbrain  contains  in  the  corpora  quad- 
rigemina  important  reflex  correlation  centers  of  sight  and  hear- 
ing, and  in  the  cerebral  peduncle  centers  for  the  coordination  of 
movements.  The  diencephalon  is  devoted  chiefly  to  various 
types  of  correlation.  It  is  divided  into  three  parts,  the  thalamus, 
the  epithalamus,  and  the  hypothalamus,  the  two  last  being 
dominated  by  the  olfactory  system.  The  thalamus  contains  a 
medial  group  of  nuclei  concerned  with  thalamic  reflexes  and  the 
affective  experience  and  a  lateral  group  of  nuclei  which  discharge 


170 


INTRODUCTION   TO   NEUROLOGY 


Gyrus  frontalis  inf. 

Gyrus  cinguli 

Corpus  callosum 

External  capsule 

Lateral  ventricle 
Caudate  nucleus 

Anterior  limb  of 
internal  capsule 

Column  of  fornix 
Lentiform  nucleus 


Posterior  limb  of 
internal  capsule 


Medial  nucleus  of 
thalamus 
Third  ventricle 

Pulvinar 

Habenula 

Lateral  ventricl 


Lateral  nucleus  of 

thalamus 
Hippocampal  com. 

Corpus  callosum 

Caudate  nucleus 

Parieto-occip.  fissure 

Cuneus 


Fig.  80.— Longitudinal  section  through  the  human  cerebral  hemisphere 
passing  through  the  internal  capsule,  some  of  the  fiber  systems  of  which  are 
numbered  as  listed  below : 

1 .  Frontal  thalamic  tracts  between  the  medial  nucleus  of  the  thalamus 
and  the  frontal  lobe  of  the  cerebral  cortex. 

2.  Frontal  pontile  tract  between  the  frontal  lobe  of  the  cortex  and  the 
pons. 

3.  Cortico-oculomotor  tract  from  the  motor  cortex  to  the  nucleus  of  the 
oculomotor  nerve. 

4.  Cortico-bulbar  tracts  from  the  motor  cortex  to  the  motor  nuclei  of  the 
medulla  oblongata. 


THE    CEREBRUM  171 

the  sensory  projection  systems  of  sight,  hearing,  and  general 
sensibility  into  the  cerebral  cortex.  The  subdivision  of  the 
diencephalon  is  summarized  in  the  table  on  p.  167.  The  cor- 
pus striatum  in  lower  vertebrates  is  an  important  reflex  center; 
in  man  its  functions  seem  to  be  subsidiary  to  those  of  the  cere- 
bral cortex  for  the  most  part.  It  consists  of  two  chief  masses  of 
gray  matter,  the  caudate  and  lentiform  nuclei,  with  sheets  of 
white  matter  between  and  within  these  masses.  The  chief  sys- 
tems of  fibers  of  the  white  matter  are  accumulated  in  the  internal 
capsule  which  lies  between  the  lentiform  nucleus  laterally  and  the 
caudate  nucleus  and  thalamus  medially.  Through  the  internal 
capsule  run  the  projection  fibers  which  connect  the  cerebral  cor- 
tex with  the  lower  parts  of  the  brain  stem,  including  the  sensory 
radiations  from  the  thalamus  and  the  descending  systems  to  the 
pons  and  brain  stem  and  the  great  pyramidal  tract,  which  is  the 
voluntary  motor  path  from  the  cortex  to  the  spinal  cord. 

Literature 

Head,  H.,  and  Holmes,  G.  1911.  Sensory  Disturbances  from  Cerebral 
Lesions,  Brain,  vol.  xxxiv,  pp.  109-254. 

Herrick,  C.  Judson.  1913.  Ai-ticle  Brain  Anatomy,  in  Wood's  Refer- 
ence Handbook  of  the  Medical  Sciences,  3d  ed.,  vol.  ii,  pp.  274-342. 

Johnston,  J.  B.  1906.  The  Nervous  System  of  Vertebrates,  Philadel- 
phia. 

v.  MoNAKOw,  C.  1895.  Experimentelle  und  pathologische-anatomische 
Untersuchungen  liber  die  Haubenregion,  den  Sehhtigel  und  die  Regio  sub- 
thalamica,  Arch.  f.  Psychiat.,  Bd.  27. 

Sachs,  E.  1909.  On  the  Structure  and  Functional  Relations  of  the  Optic 
Thalamus,  Brain,  vol.  xxxii,  pp.  95-186. 

5.  Cortico-rubric  tract  from  the  motor  cortex  to  the  nucleus  ruber. 

6  to  10.  Pyramidal  tract  (tractus  cortico-spinaUs)  from  the  jnotor  cortex 
to  the  spinal  cord,  with  the  following  parts — 

6.  To  the  cervical  spinal  cord  for  the  muscles  of  the  shoulder. 

7.  To  the  cervical  cord  for  the  muscles  of  the  arm. 

8.  To  the  cervical  cord  for  the  muscles  of  the  hand. 

9.  To  the  lumbar  cord  for  the  muscles  of  the  leg. 

10.  To  the  lumbar  cord  for  the  muscles  of  the  foot. 

11.  Somesthetic  radiations  from  the  lateral  and  ventral  nuclei  of  the 
thalamus  to  the  cerebral  cortex. 

12.  Occipito-temporal  pontile  tract  to  the  pons,  and  temporo-thalamic 
tract  to  the  thalamus. 

13.  Auditory  radiation  from  the  medial  geniculate  body  to  the  superior 
temporal  gyrus. 

14.  Optic  radiation  from  the  pulvinar  and  lateral  geniculate  body  to  the 
cuneus  in  the  occipital  lobe  of  the  cortex. 


CHAPTER  XI 

THE  GENERAL  SOMATIC  SYSTEMS  OF  CONDUCTION 

PATHS 

In  this  and  the  following  chapters  we  shall  review  the  con- 
duction pathways  followed  by  some  of  the  chief  sensori-motor 
systems  and  add  some  further  details  to  the  general  description 
already  given,  beginning  with  the  more  generalized  somatic 
sensory  functions. 

Clinical  neurologists  have  long  been  in  the  habit  of  grouping 
together  the  different  forms  of  deep  and  cutaneous  sensibility 
under  the  term  "general  sensibility."  The  more  refined  re- 
searches of  recent  students  (especially  Sherrington,  Head, 
Trotter  and  Davies,  Brouwer,  see  the  bibliographies  on  pp. 
94  and  142)  have  given  us  a  much  more  precise  analysis 
of  these  systems,  as  already  explained.  The  peripheral 
nerves  of  deep  sensibility  (exclusive  of  those  devoted  to 
strictly  visceral  functions)  are  anatomically  distinct  from 
those  of  cutaneous  sensibility.  Physiologically,  the  nerves  of 
deep  sensibility  are  devoted  chiefly  to  proprioceptive  functions 
(muscle  sensibility,  joint  sensibihty,  etc.),  and  the  nerves  of 
cutaneous  sensibility  chiefly  to  exteroceptive  functions  (touch, 
temperature,  and  pain);  but  this  holds  only  approximately,  for 
nerves  of  deep  sensibility  may  also  serve  the  exteroceptive  func- 
tions of  pressure  and  painful  response  to  overstimulation, 
though  with  a  higher  stimulus  threshold  than  in  the  skin,  and  the 
cutaneous  nerves  also  participate  to  some  extent  in  the  proprio- 
ceptive functions  of  spatial  orientation  of  the  body  and  its  mem- 
bers (see  pp.  77  ff.  and  132). 

Exteroceptive  Systems. — The  nerves  serving  the  functions 
of  touch,  pressure,  temperature,  and  pain  of  the  body  and 
limbs,  whether  derived  from  the  skin  or  the  deep  tissues,  im- 
mediately after  their  entrance  into  the  spinal  cord  terminate  in 

172 


GENERAL    SOMATIC    SYSTEMS    OF    CONDUCTION    PATHS      173 

the  gray  matter  of  the  dorsal  column  of  the  same  side.  After 
a  synapse  here  the  axons  of  the  neurons  of  the  second  order  cross 
to  the  opposite  side  of  the  cord  and  ascend  in  the  spinal  lemniscus 
to  the  thalamus.  For  further  details  of  these  connections  see 
pages  138-140,  163-169,  and  Figs.  59,  63,  64,  75,  77,  78,  80,  81; 
on  the  pain  path,  see  also  p.  251.  The  pathway  for  cutaneous 
sensibility  from  the  head  follows  the  trigeminal  lemniscus  (pp. 
157,  180,  and  Figs.  64,  75,  77,  78,  81).  The  more  important 
exteroceptive  pathways  are  assembled  in  Fig.  81. 

It  will  be  recalled  that  in  the  spinal  lemniscus  the  pathways  for 
touch  and  pressure,  for  pain  and  for  temperature  are  assembled 
in  three  distinct  tracts,  those  for  pain  and  temperature  being 
close  together  (Fig.  63,  p.  139).  From  this  it  follows  that  small 
circumscribed  injuries  in  the  white  substance  of  the  spinal  cord 
may  destroy  all  sensibility  to  pressure  in  a  part  of  the  body  with- 
out any  disturbance  whatever  of  pain  or  temperature  sensibility, 
or  conversely,  it  may  destroy  pain  or  temperature  sensibility 
without  any  involvement  of  the  other  qualities  of  sensation. 
And,  in  fact,  in  numerous  clinical  cases  these  conditions  are 
found,  as  will  be  clear  from  the  following  example. 

Figure  82  illustrates  such  a  case  from  Dr.  Head's  experience. 
The  patient  suffered  from  an  injury  to  the  lower  part  of  the 
spinal  cord  caused  by  the  overturning  of  a  truck  of  concrete, 
and  when  admitted  to  the  London  Hospital  was  paralyzed  from 
the  hips  downward.  In  the  course  of  a  year  he  partly  recovered, 
but  showed  a  permanent  loss  of  some  sensation  qualities  over 
the  shaded  area  in  the  figure.  The  right  leg  below  the  knee  was 
insensitive  to  pain  (prick)  and  to  all  degrees  of  temperature. 
But  over  the  whole  of  this  area  he  could  appreciate  all  tactile 
stimuli  and  could  localize  accurately  the  spot  touched  or  pressed 
upon.  Yet  it  was  not  possible  to  produce  pain  anywhere  over 
the  right  leg  and  foot  by  excessive  pressure,  although  he  fully 
recognized  its  gradual  increase.  Referring  to  Fig.  63  (p.  139), 
it  is  evident  that  to  produce  these  symptoms  the  lesion  must 
have  involved  the  conduction  path  for  pain  and  temperature  in 
the  lateral  funiculus  (fiber  8  of  the  figure)  of  the  left  side  of  the 
spinal  cord,  and  spared  the  path  for  touch  and  pressure  in  the 
ventral  funiculus  (fiber  9).  Both  superficial  pain  (prick)  and 
deep  pain  caused  by  excessive  pressure  were  abolished.     This 


174 


INTRODUCTION   TO    NEUROLOGY 


to  cor^en 


sublhalamus 

trigeminol 
lemniscus 


lateral  lemniscus 
medial  lemniscusj 


Vnerve 
Vnudeus 


spinal  V Tract 
reTicular  formaTion 


spinalY  tract- 


spinalYnudeus 


-6.  Touch  and  pressure 
\\—7.  poin  and  lemprature 
-'}  spinal  lemniscus 


Fig.  81. — Diagram  of  the  exteroceptive  conduction  pathways  contained 
within  the  spinal  cord  and  brain  stem.  The  figure  illustrates  cross-sections 
of  the  central  nervous  system  in  the  lower  cervical  region  of  the  spinal 
cord,  at  the  level  where  the  cord  passes  over  into  the  medulla  oblongata,  at 
the  level  of  the  roots  of  the  VIII  cranial  nerve,  through  the  inferior  collicu- 
lus  and  through  the  thalamus. 

1.  Connections  of  peripheral  neuron  of  touch,  temperature,  or  pain  for 
intrinsic  spinal  reflexes. 


GENERAL    SOMATIC    SYSTEMS    OF    CONDUCTION    PATHS       175 

combination  of  symptoms  could  not  be  produced  by  any  injury 
to  the  nerve-roots  or  peripheral  branches. 

Proprioceptive  Systems. — Referring  back  to  p.  137,  we  are 
reminded  that  the  ascending  proprioceptive  fibers  of  the  spinal 
cord  effect  three  types  of  connections  within  the  brain:  (1)  in 


Fig.  82. — The  sensory  loss  resulting  from  an  injury  to  the  lower  part  of 
the  spinal  cord.  The  shaded  area  represents  the  parts  insensitive  to  cuta- 
neous painful  stimuli  and  also  to  the  pain  of  excessive  pressure;  yet  over  this 
area  Hght  touch  and  the  tactile  element  of  pressure  were  appreciated. 
(After  Head  and  Thompson.) 

the  cerebellum;  (2)  in  the  brain  stem;  (3)  in  the  cerebral  cortex. 
The  connections  of  the  second  and  third  types  are  made  through 
the  dorsal  funiculus  and  medial  lemniscus;  they  are  shown  in 

2.  Peripheral  neuron  of  pain  or  temperature. 

3.  Peripheral  neuron  of  touch  and  pressure. 

4.  Peripheral  motor  neurons  of  spinal  nerve. 

5.  Peripheral  cutaneous  neuron  of  trigeminal  nerve. 

6.  Secondary  neuron  of  touch  and  pressure  in  spinal  lemniscus. 

7.  Secondary  neuron  of  pain  or  temperature  in  spinal  lemniscus. 

8.  Secondary  neuron  from  lower  part  of  spinal  V  nucleus  entering  the 
spinal  lemniscus. 

9.  Secondary  neuron  from  chief  sensory  V  nucleus  entering  the  trigemi- 
nal lemniscus. 

10.  Intrinsic  correlation  neuron  of  thalamus  for  thalamic  reflexes. 

11,  12,  13.  Thalamo-cortical  radiations  to  the  postcentral  gyrus. 


176 


INTRODUCTION   TO    NEUROLOGY 


subthalQmus^-^P°'^^'^-  [—7 


^^\ 


veslibula 
nerve 
11 


vestibulo- 
spinal tract,  16 


dorsol  spino- 
cerebellar tract,  7- 


c 


-21.  tecto- cerebellar  Trad 


-to  cerebellum 
(brochium  conjunctivumj 


•  it;  longitudinal   medial 

fasciculus 


-to  cerebellum 
(corpus  restiforme) 


-reticular  formation 


dial  lemniscus 


-  nucleus  of  fasc.  gracilis 
■  nucleus  of  fasccuneafus 


-6,spino-olivary  tract 
-5,ventral  spino-  cerebellar  trad 


Fig.  83. — Diagram  of  the  chief  proprioceptive  conduction  pathways  con- 
tained within  the  spinal  cord  and  brain  stem.  The  mesencephahc  root  of 
the  trigeminal  nerve  (see  p.  180  and  Figs.  71  and  77)  is  omitted  and  not  all 
of  the  cerebellar  connections  are  indicated.  The  connection  to  the  cere- 
bellum from  the  nuclei  of  the  fasciculi  gracilis  and  cuneatus  (neuron  14)  is 
controverted,  but  it  is  well  established  that  similar  connections  are  effected 
immediately  below  this  level  from  the  dorsal  funiculus  of  the  cord.  The 
figure  illustrates  cross-sections  of  the  central  nervous  system  m  the  lower 
cervical  region  of  the  spinal  cord,  at  the  level  where  the  cord  passes  over 


GENERAL    SOMATIC    SYSTEMS    OF    CONDUCTION    PATHS       177 

Figs.  59,  63,  64,  75,  77,  78,  and  80,  and  in  a  more  comprehensive 
way  in  Fig.  83. 

The  cortical  proprioceptive  pathway  in  its  simplest  form  may 
consist  of  a  chain  of  only  three  neurons:  (1)  A  peripheral  neuron 
whose  cell  body  lies  in  some  spinal  ganglion,  whose  dendrite 
reaches  some  organ  of  muscle  sense,  tendon  sense,  or  similar 
receptor,  and  whose  axon  terminates  at  the  upper  end  of  the  cord 
in  the  nucleus  of  the  fasciculus  gracilis  or  fasciculus  cuneatus  of 
the  same  side;  (2)  the  body  of  the  second  neuron  lies  in  one  of 
the  nuclei  last  mentioned  (marked  nucleus  of  dorsal  funiculus  in 
Fig.  64),  its  axon  ascends  in  the  medial  lemniscus,  and  termi- 
nates in  the  lateral  and  ventral  nuclei  of  the  thalamus  of  the 
opposite  side  (Figs.  77  and  83) ;  (3)  the  neuron  of  the  third  order 
lies  in  the  thalamus  and  sends  its  axon  through  the  internal  cap- 
sule to  the  somesthetic  area  of  the  cerebral  cortex. 

The  dorsal  funiculi  of  the  spinal  cord  have  until  recently  been 
regarded  as  the  chief  ascending  pathway  for  all  forms  of  sensi- 
bility, and  much  of  the  clinical  practice  now  in  vogue  is  based 
upon  this  assumption.  But  evidently  such  an  assumption  is 
untenable.     The  dorsal  funiculi  seem  to  be  concerned  chiefly 


into  the  medulla  oblongata,  at  the  level  of  the  roots  of  the  VIII  cranial 
nerve,  through  the  inferior  colliculus,  and  through  the  thalamus. 

1.  Peripheral  neuron  entering  the  dorsal  funiculus  and  also  effecting 
intrinsic  spinal  reflex  connections. 

2.  Peripheral  neuron  entering  the  nucleus  dorsalis  of  Clarke. 

3.  Peripheral  neuron  effecting  connections  with  the  intrinsic  correla- 
tion neurons  of  the  spinal  cord. 

4.  Peripheral  motor  neurons  of  spinal  nerve. 

5.  Ventral  spino-cerebellar  tract. 

6.  Spino-oUvary  tract. 

7.  Dorsal  spino-cerebellar  tract. 

8.  9.  Medial  lemniscus. 

10.  Vestibular  root  fiber  passing  directly  into  the  cerebellum. 

11.  Vestibular  root  fiber  entering  the  vestibular  nucleus. 

12.  Vestibulo-cerebellar  tract. 

13.  Olivo-cerebellar-tract. 

14.  Path  from  the  dorsal  funiculus  (or  its  nuclei)  to  the  cerebellum. 

15.  Path  from  the  reticular  formation  to  the  cerebellum. 

16.  Vestibulo-spinal  tract. 

17.  Path  from  the  vestibular  nucleus  to  the  fasciculus  longitudinalis 
medialis. 

18.  Path  from  the  vestibular  nucleus  to  the  reticular  formation. 

19.  20.  Thalamic  radiations  to  the  cerebral  cortex. 
21.  Tecto-cerebellar  tract. 

12 


178  INTRODUCTION  TO  NEUROLOGY 

with  the  proprioceptive  group  of  reactions.  These  may  be 
unconscious  reflexes  of  motor  coordination  and  the  maintenance 
of  equihbrium,  or  they  may  come  into  consciousness  as  sensa- 
tions of  position  and  orientation  of  the  body  and  its  parts  and  of 
spatial  discrimination.  Purely  exteroceptive  stimuli,  whether 
transmitted  by  the  deep  nerves  or  by  the  cutaneous  nerves,  may 
be  carried  for  a  few  segments  in  the  dorsal  funiculi  (Fig.  81, 
neuron  1);  but  they  are  soon  filtered  off  into  the  gray  matter  of 
the  dorsal  column,  and  after  a  synapse  here  they  are  sorted  into 
functionally  distinct  tracts  on  the  opposite  side  of  the  cord. 
The  tactile  elements  of  the  mixed  peripheral  root  fibers  entering 
the  dorsal  funiculus  are  drawn  off  later  than  are  the  elements  for 
thermal  and  painful  sensibility;  and  some  of  the  components 
commonly  reckoned  with  cutaneous  exteroceptive  sensibility 
remain  in  the  dorsal  funiculus  for  its  entire  length.  These  are 
chiefly  two-point  discrimination,  and  discrimination  of  size, 
shape,  form,  and  texture  of  surfaces.  These  all  involve  a  com- 
parison and  discrimination  in  consciousness  of  spatial  factors 
and  are,  therefore,  bound  up  with  those  fibers  which  serve  the 
proprioceptive  reflexes,  which  are  unconscious  spatial  adjust- 
ments. 

Some  peculiar  combinations  of  symptoms  arise  from  the  fact 
that,  whereas  the  ascending  proprioceptive  impulses  (so  far  as 
these  are  consciously  perceived)  pass  up  in  the  dorsal  funiculus 
of  the  same  side  for  the  entire  length  of  the  cord,  the  impulses 
of  the  exteroceptive  impulses,  within  a  few  segments  of  their 
point  of  entrance  into  the  cord,  are  transferred  to  the  opposite 
side  to  ascend  in  the  spinal  lemniscus  tracts.  From  this  it  fol- 
lows that  a  localized  central  injury  involving  the  dorsal  gray 
column  and  dorsal  funiculus  of  one  side  only  will  cut  off  all 
ascending  proprioceptive  impulses  which  pass  through  the  dor- 
sal funiculus  from  lower  levels  on  the  same  side  of  the  body  as  the 
lesion,  and  at  the  same  time  will  abolish  both  proprioceptive  and 
exteroceptive  functions  in  a  circumscribed  region  of  the  same 
side  of  the  body  whose  exteroceptive  neurons  of  the  first  order 
discharge  into  the  injured  part  of  the  dorsal  gray  column. 

Figure  84  illustrates  the  loss  of  sensibility  to  painful  stimuli 
resulting  from  a  tumor  in  the  cervical  region  of  the  spinal  cord. 
Tactile,  temperature,  and  deep  sensibility  were  also  profoundly 


GENERAL    SOMATIC    SYSTEMS    OF    CONDUCTION    PATHS       179 

disturbed  over  approximately  the  same  region  (the  temperature 
disturbance  involving  the  right  side  also).  These  symptoms 
resulted  from  the  destruction  of  all  dorsal  root  fibers  in  the 
affected  area  at  the  point  of  their  entrance  into  the  cord  or  of  the 
gray  substance  containing  the  terminals  of  these  fibers,  a  purely 
local  effect.  That  the  dorsal  funiculus  of  the  same  side  was  also 
involved  is  shown  by  symptoms  of  remote  effects  of  the  injury 
in  the  left  foot.  All  forms  of  exteroceptive  sensibility  (touch, 
temperature,  pain)  were  perfectly  preserved  in  both  legs,  but  the 
left  leg  was  devoid  of  proprioceptive  sensibility,  as  shown  by  the 


Fig.  84. — The  loss  of  sensibility  to  pain  resulting  from  a  tumor  in  the  cervical 
region  of  the  spinal  cord.     (After  Head  and  Thompson.) 

loss  of  ability  to  appreciate  the  passive  position  or  movement  of 
the  leg  and  failure  to  discriminate  two  points  with  the  compass 
test. 

The  intrinsic  connections  within  the  cord  for  spinal  reflexes  are  undoubt- 
edly very  primitive.  These  are  both  exteroceptive  and  proprioceptive  in 
type  (p.  132).  We  have  seen  that  the  ascending  tracts  between  the  spinal 
cord  and  the  brain  fall  into  two  groups:  (1)  The  exteroceptive  systems  in 
the  spinal  lemniscus,  and  (2)  the  proprioceptive  systems  in  the  dorsal  funicu- 
lus and  medial  lemniscus.  Comparative  anatomy  shows  that  the  spinal 
lemniscus  system  is  much  older  phylogenetically  than  the  medial  lemniscus 
system.  The  fishes  possess  well-defined  spino-tectal  and  spino-thalamic 
tracts,  but  their  dorsal  funiculus  possesses  only  the  fasciculus  proprius 


180  INTRODUCTION  TO  NEUROLOGY 

fibers  (cf.  Figs.  66,  67,  pp.  150,  151)  and  they  lack  the  medial  lemniscus 
altogether.  The  spino-cerebellar  tracts,  on  the  other  hand,  are  very  ancient 
and  are  present  from  the  lowest  to  the  highest  vertebrates. 

These  considerations  suggest  that  the  first  fibers  to  pass  from  the  spinal 
cord  to  the  higher  centers  of  the  brain,  and  presumably  the  first  sensory 
impulses  from  the  spinal  nerves  to  be  consciously  perceived,  were  those  of 
touch  and  temperature  transmitted  through  the  spinal  lemniscus.  (Pain 
is  probably  also  very  primitive  as  a  conscious  experience,  but  it  is  doubtful 
whether  it  is  represented  in  the  spinal  lemniscus  of  lower  forms;  see  p.  251). 
The  proprioceptive  impulses  in  lower  vertebrates  are  coordinated  quite  un- 
consciously in  the  brain  stem  and  cerebellum,  and  it  is  only  in  the  higher 
forms  that  this  system  of  nervous  impulses  reaches  the  thalamus  (through 
the  medial  lemniscus)  and  cerebral  cortex  for  conscious  control.  CHnical 
evidence  shows  that  the  medial  lemniscus  connections  in  man  are  concerned 
with  the  conscious  adjustments  of  the  positions  and  orientation  in  space  of 
the  body  and  its  members  and  with  spatial  discriminations  of  various  sorts, 
rather  than  with  the  senses  of  touch  and  pressure  as  externally  projected. 

The  innervation  of  the  organs  of  muscular  sensibility  and  tendon  sensi- 
bility in  the  head  is  not  as  fully  known  as  in  the  case  of  those  of  the  trunk 
and  limbs,  as  above  described.  Sherrington  and  Tozer  have  recently 
shown  that  such  organs  are  present  in  the  muscles  which  move  the  eyeball 
and  that  their  nerves  accompany  the  motor  fibers  of  the  III,  IV,  and  VI 
cranial  nerves;  but  of  the  central  connections  of  these  sensory  nerve-fibers 
of  the  eye  muscles  nothing  is  known.  It  is  suggested  by  the  researches  of 
Johnston,  Willems,  and  many  others  that  the  jaw  muscles,  which  receive 
their  motor  innervation  from  the  motor  V  nucleus  (nucleus  masticatorius), 
receive  their  sensory  innervation  from  the  mesencephalic  nucleus  of  the  V 
nerve,  whose  position  along  the  lateral  border  of  the  aqueduct  of  Sylvius 
is  seen  in  Figs.  71,  75,  and  77.  But  recent  studies  of  Edgeworth_  have 
shown  that  these  muscles  also  receive  sensory  fibers  from  the  semilunar 
or  Gasserian  ganglion  of  the  V  nerve,  and  the  question  requires  further  inves- 
tigation. Possibly  the  sensory  fibers  from  the  Gasserian  ganglion  to  the 
muscular  branches  of  the  V  nerve  conduct  impressions  of  deep  sensibility 
of  pressure  and  pain  of  the  exteroceptive  type,  while  those  from  the  mesen- 
cephalic V  nucleus  innervate  the  muscle  spindles  for  true  proprioceptive 
sensibility. 

The  fibers  of  the  chief  sensory  root  of  the  V  nerve  in  part  end  in  the  chief 
sensory  V  nucleus  near  the  level  of  their  entrance  into  the  medulla  oblongata 
(Figs.  71,  77)  and  in  part  pass  downward  through  the  whole  length  of  the 
medulla  oblongata  and  upper  levels  of  the  spinal  cord  as  the  spinal  V  tract 
(Figs.  64,  71,  72,  81).  It  is  suggested  by  clinical  and  comparative  evidence 
that  the  spinal  V  tract  and  its  nucleus  are  connected  with  a  phylogenetically 
old  type  of  reaction  to  touch,  temperature,  and  pain,  probably  chiefly  reflex, 
while  the  chief  nucleus  is  concerned  with  the  more  recently  acquired  dis- 
criminations of  these  systems  with  more  direct  cortical  connections.  The 
fibers  of  the  trigeminal  lemniscus  (p.  157)  follow  two  separate  tracts  arising 
from  these  two  parts  of  the  sensory  V  nucleus,  only  the  upper  one  of  which 
is  shown  in  Fig.  77,  though  both  are  shown  in  Fig.  81  (neurons  8  and  9). 

Motor  Paths. — Throughout  the  length  of  the  spinal  cord  and 
brain  stem  the  ascending  fibers  of  both  exteroceptive  and  pro- 
prioceptive sensibility  give  off  collateral  branches  into  the  reticu- 


GENERAL    SOMATIC    SYSTEMS    OF    CONDUCTION    PATHS      181 

lar  formation  (p.  158)  for  reflex  connections  with  the  motor 
nuclei  at  various  levels.  The  arrangement  of  these  motor  nuclei 
of  the  brain  stem,  from  which  peripheral  motor  fibers  of  the 
cranial  nerves  arise,  is  shown  on  the  left  side  of  Fig.  71  (p.  154). 
The  details  of  these  connections  for  local  motor  reflexes  will  not 
be  entered  into  here.  From  the  ventral  part  of  the  thalamus 
(p.  163)  there  are  descending  thalamo-bulbar  and  thalamo- 
spinal  tracts  for  local  thalamic  reflexes.  The  main  descending 
pathway  for  voluntary  motor  responses  to  general  somatic 
stimuli  arises  from  the  precentral  gyrus  of  the  cerebral  cortex 
(p.  283).  This  is  the  tractus  cortico-bulbaris  (Fig.  75)  and  trac- 
tus  cortico-spinalis  or  pyramidal  tract  (Figs.  64,  75,  137).  The 
reflex  connections  effected  in  the  medulla  oblongata  are  some- 
what more  complex  than  those  of  the  spinal  cord,  that  is,  they 
represent  the  integration  of  more  different  kinds  of  sensory  im- 
pulses and  facilitate  the  performance  of  a  greater  variety  of 
movements  by  way  of  response.  Similarly,  the  complexity  of 
the  reflex  adjustments  increases  as  we  pass  forward  into  the  mid- 
brain, thalamus,  and  cerebral  cortex  (see  p.  63). 

Attention  has  already  been  called  to  the  fact  that  the  centers  of  adjust- 
ment in  the  brain  stem  are  of  two  physiologically  different  types  which  we 
have  termed  centers  of  correlation  and  centers  of  coordination  (p.  35).  The 
more  labile  and  individually  variable  adjustments  are  effected  in  the  corre- 
lation centers  which  are  developed  from  the  more  dorsal  parts  of  the  embry- 
onic neural  tube  above  the  limiting  sulcus  (p.  120),  while  the  more  ventral 
parts  of  the  neural  tube  give  rise  to  the  motor  centers  and  the  centers  of  co- 
ordination, whose  adjustments  are  of  a  more  fixed  and  invariable  character. 
In  the  embryonic  development  the  coordination  centers  develop  preco- 
ciously, while  the  correlation  centers  mature  more  slowly;  the  higher  asso- 
ciation centers  of  the  thalamus  and  cerebral  cortex  in  particular  are  the  last 
to  mature  (p.  286). 

In  the  phylogenetic  development  of  the  brain  the  same  rule  holds.  In 
the  lowest  vertebrates  the  coordination  centers  are  much  larger  in  pro- 
portion to  the  size  of  the  correlation  centers  than  in  higher  vertebrates. 
Bartlemez^  has  analyzed  these  motor  coordination  mechanisms  (which  he 
terms  in  the  aggregate  the  nucleus  motorius  tegmenti)  in  fishes,  and  finds  in 
the  motor  tegmentum  throughout  the  medulla  oblongata  a  nucleus  of  a 
primitive  type  whose  neurons  serve  to  connect  the  primary  sensory  nuclei 
with  the  primary  motor  nuclei.  Some  of  these  connections  are  very  short, 
while  others  are  very  long,  reaching  remote  parts  of  the  brain  and  spinal 
cord  through  the  longitudinal  medial  fasciculus  (pp.  185,  211).  This  nu- 
cleus is  the  parent  tissue  out  of  which  the  more  complex  coordination  centers 
in  the  tegmentum  of  higher  vertebrates  have  been  differentiated. 

1  Bartlemez,  G.  W.  1915.  Mauthner's  Cell  and  the  Nucleus  Motorius 
Tegmenti,  Jour.  Comp.  Neur.,  vol.  xxv,  pp.  87-128. 


182  INTRODUCTION  TO  NEUROLOGY 

In  very  young  amphibian  embryos  Coghill^  finds  a  still  simpler  condition 
which  is  probably  also  more  primitive.  In  the  spinal  cords  of  these  larvae 
the  individual  neurons  of  the  motor  tegmentum  give  rise  both  to  fibers  of  the 
longitudinal  conduction  tract  of  motor  coordination  (fasciculus  proprius 
ventraUs)  and  to  peripheral  fibers  of  the  ventral  roots,  the  latter  arising  as 
collaterals  of  the  longitudinal  axons.  In  older  larvae  separate  neurons  have 
been  differentiated  for  these  two  functions  of  peripheral  conduction  and 
longitudinal  conduction.  The  steps  in  the  embryologic  development  and 
probable  evolution  of  the  more  complex  centers  of  adjustment  have  been 
briefly  reviewed  by  Herrick  and  Coghill  (see  p.  66). 

Summary. — The  old  clinical  concept  "general  sensibility" 
has  recently  been  analyzed  into  a  number  of  components,  the 
most  fundamental  division  being  the  distinction  between  a 
group  of  exteroceptive  and  a  group  of  proprioceptive  systems. 
The  exteroceptive  systems  are  transmitted  from  the  spinal 
cord  to  the  brain  through  a  complex  tract,  the  spinal  lemniscus, 
within  which  there  are  separate  pathways  for  the  three  qualities 
of  sensation,  touch,  temperature,  and  pain.  These  sensation 
qualities  come  into  consciousness  with  a  distinct  peripheral  or 
external  reference.  The  proprioceptive  systems  (muscle  sense 
and  allied  types)  are  transmitted  to  the  brain  through  the  dorsal 
funiculus  of  the  same  side  of  the  cord,  the  medial  lemniscus  of 
the  opposite  side,  the  thalamus,  and  the  somesthetic  radiations 
to  the  cerebral  cortex;  and  also  through  the  spino-cerebellar 
tracts  to  the  cerebellar  cortex.  Most  of  these  reactions  of 
spatial  adjustment  do  not  come  into  consciousness  at  all,  but 
some  appear  subjectively  as  sensations  of  posture,  bodily  move- 
ment, and  spatial  discrimination.  The  cerebellum  is  the  great 
clearing  house  for  these  and  all  other  afferent  systems  which 
are  concerned  in  the  proprioceptive  functions,  so  far  as  these  are 
unconsciously  performed. 

1  Coghill,  G.  E.  1913.  The  Primary  Ventral  Roots  and  Somatic  Motor 
Column  of  Amblystoma,  Jour.  Comp.  Neur.,  vol.  xxiii,  pp.  121-144. 

— .  1914.  Correlated  Anatomical  and  Physiological  Studies  of  the 
Growth  of  the  Nervous  System  of  Amphibia,  Jour.  Comp.  Neur.,  vol.  xxiv, 
pp. 161-233. 


CHAPTER  XII 

THE  VESTIBULAR  APPARATUS  AND  CEREBELLUM 

The  general  somatic  sensory  systems  considered  in  the  last 
chapter  include  some  of  the  most  primitive  reflex  mechanisms. 
These  fall  into  two  groups — the  exteroceptive  systems  and  the 
proprioceptive  systems  (pp.  77-89) — and  each  of  these  groups 
comprises,  in  addition  to  its  primitive  generalized  members, 
certain  so-called  organs  of  special  or  higher  sense.  The  special 
exteroceptive  sense  organs  are  the  organ  of  hearing  (p.  195) 
and  the  organ  of  vision  (p.  204).  The  special  proprioceptive 
sense  organs  are  the  semicircular  canals  of  the  internal  ear;  and 
those  will  next  be  described,  together  with  their  central  mechan- 
isms in  the  medulla  oblongata  and  cerebellum. 

The  Vestibular  Apparatus. — The  internal  ear  contains  two 
quite  distinct  groups  of  sense  organs,  the  organ  of  hearing  in  the 
cochlea  and  the  vestibular  organs  (utricle,  saccule,  and  semicircu- 
lar canals) ,  both  of  which  are  supplied  by  the  VIII  cranial  nerve, 
which  accordingly  has  two  parts,  the  cochlear  and  the  vestibu- 
lar nerves.  The  semicircular  canals  are  the  most  highly  spe- 
cialized end-organs  of  the  proprioceptive  series  and  are  con- 
cerned chiefly  with  the  maintenance  of  bodily  equilibrium.  The 
general  structure  of  the  internal  ear  is  described  on  p.  195;  here 
we  need  merely  mention  that  the  three  semicircular  canals 
(ductus  semicirculares)  of  each  ear  lie  approximately  at  right 
angles  to  each  other,  as  shown  diagrammatically  in  Fig.  85,  and 
each  canal  is  dilated  at  one  end  to  form  the  ampulla,  within 
which  is  a  patch  of  sensory  epithelium  from  which  hairs  project 
into  the  contained  fluid  (see  Figs.  32  and  91).  A  movement  of 
the  head  in  any  direction  will  cause  a  flow  of  the  fluid  in  one  or 
more  of  these  canals  in  each  ear,  which  in  turn  will  excite  a 
nervous  impulse  in  the  hair-cells  of  the  corresponding  ampullse. 
These  nervous  impulses  will  be  transmitted  to  the  vestibular 
centers  of  the  brain,  where  they  will  be  so  analyzed  as  to  call  forth 

183 


184  INTRODUCTION  TO  NEUROLOGY 

the  appropriate  reaction  to  the  movement  which  has  excited  the 
particular  semicircular  canals  involved. 

The  fibers  of  the  vestibular  nerve  enter  the  medulla  oblongata 
immediately  behind  the  pons  and  terminate  in  a  vestibular  nu- 


Fig.  85. — Diagram  of  the  position  of  the  semicircular  canals  in  the  head, 
as  seen  from  behind.  On  each  side  it  will  be  seen  that  the  three  canals  lie 
in  planes  at  right  angles  to  one  another.  The  external  or  horizontal  canals 
(E)  of  the  two  sides  lie  in  the  same  plane.  The  anterior  canal  of  one  side 
(A)  hes  in  a  plane  parallel  to  that  of  the  posterior  canal  (P)  of  the  other 
side.     (After  Ewald.) 

cleus  which  forms  an  eminence  on  the  floor  of  the  fourth  ventricle 
in  this  region  (Figs.  71,  96).  This  nucleus  has  four  subdivisions, 
as  follows: 

Nucleus  nervi  vestibuU  medialis  (of  Schwalbe,  also  called  nucleus  dor- 

salis  and  principal  nucleus). 
Nucleus  nervi  vestibuli  lateralis  (of  Deiters). 
Nucleus  nervi  vestibuli  superior  (of  Bechterew). 
Nucleus  nervi  vestibuli  spinalis. 

The  arrangement  of  these  nuclei  and  of  some  of  their  second- 
ary connections  is  shown  in  Fig.  86.  Some  of  these  connections 
are  made  with  the  motor  nuclei  and  reticular  formation  of  the 


THE    VESTIBULAR    APPARATUS    AND    CEREBELLUM 


185 


medulla  oblongata  for  local  bulbar  reflexes;  there  is  a  vestibulo- 
spinal tract  (tr.v.sp.)  for  movements  of  the  trunk  and  limbs 


ereb 


V.  sp. 
,Tn. 


Fig.  86. — Diagram  of  the  nuclei  of  the  vestibular  nerve,  together  with 
some  of  the  associated  fiber  tracts.  The  secondary  tracts  associated  with 
the  vestibular  nuclei  are  drawn  in  full  lines ;  a  part  of  the  secondary  auditory 
path  from  the  cochlear  nuclei  is  drawn  in  broken  lines.  Compare  Figs. 
71, 77,  96.  br.c.inf.,  brachium  quadrigeminmn  inferius;  c.g.m.,  corpus  genic- 
ulatum  mediale;  collie,  inf.,  coUiculus  inferior;  collie,  sup.,  colliculus  superior; 
f.l.m.,  fasciculus  longitudinahs  medialis;  L,  nucleus  nervi  vestibuli  lateralis 
(Deiters);  Im.  lat.,  lemniscus  lateralis;  M,  nucleus  nervi  vestibuli  medialis 
(Schwalbe);  n.lm.  lat.,  nucleus  of  lemniscus  lateralis;  7iue.  amh.,  nucleus 
ambiguus;  ol.  sup.,  superior  olive;  *S,  nucleus  nervi  vestibuli  superior  (Bech- 
terew);  Sp.,  nucleus  spinalis  nervi  vestibuli;  tr.  v.  cercb.,  tractus  vcstibulo- 
cerebellaris ;  tr.v.sp.,  tractus  vestibulo-spinalis;  VIII  c,  radix  cochlearis  of 
VIII  nerve;  VIII  v.,  radix  vestibularis  of  VIII  nerve. 

in  response  to  stimulation  of  the  semicircular  canals;  and  there 
is  also  a  strong  connection  with  the  longitudinal  medial  fascicu- 


186  INTRODUCTION  TO  NEUROLOGY 

lus  (f.l.m.),  by  which  fibers  descend  to  the  spinal  cord  (chiefly 
for  turning  movements  of  the  head  by  the  neck  muscles)  and 
ascend  to  the  midbrain.  The  last-mentioned  fibers  connect 
chiefly  with  the  nuclei  of  the  motor  nerves  for  the  eye  muscles 
(III,  IV,  and  VI  pairs  of  cranial  nerves),  thus  providing  for 
the  conjugate  movements  of  the  eyes  which  accompany  head 
movements  (in  this  way,  for  instance,  enabling  one  to  keep  the 
gaze  fixed  upon  a  stationary  object  while  the  head  is  moving, 
cf.  p.  211). 

It  will  be  noticed  that  there  is  no  important  pathway  from 
the  vestibular  nucleus  to  the  thalamus  and  cerebral  cortex,  for 
the  equilibratory  reactions  excited  from  the  semicircular  canals 
are  normally  unconsciously  performed.  This  is  in  marked 
contrast  with  the  connections  of  the  cochlear  nerve,  for  the  audi- 
tory reactions  are  often  consciously  directed  (p.  202).  There 
is,  however,  an  important  connection  with  the  cerebellum, 
partly  directly  by  root  fibers  of  the  vestibular  nerve  and  partly 
by  secondary  fibers  from  the  superior  and  lateral  vestibular 
nuclei  (Fig.  86).  The  cerebellum  is,  accordingly,  an  important 
center  of  adjustment  for  the  proprioceptive  reflexes,  and  to  this 
our  attention  will  next  be  directed. 

The  Cerebellum. — This  important  organ  is  an  overlord  which 
dominates  the  proprioceptive  functions  of  the  body  in  some- 
what the  same  way  that  the  cerebral  cortex  directs  and  controls 
the  exteroceptive  reactions.  Both  of  these  organs  are  second- 
arily added  to  the  more  primitive  segmental  structures  of  the 
brain  stem,  that  is,  they  are  suprasegmental  (p.  113). 

The  correlation  centers  of  the  brain  stem,  and  particularly 
those  of  the  cerebral  cortex,  analyze  the  afferent  impulses  enter- 
ing the  brain  and  determine  what  particular  reactions  are  ap- 
propriate in  each  situation.  After  the  character  of  the  move- 
ment has  been  determined  in  this  way,  the  proprioceptive  sys- 
tems cooperate  in  its  execution,  and  the  cerebellum  is  the  cen- 
tral coordination  station  for  the  proprioceptive  reactions. 
None  of  its  activities  come  into  consciousness. 

The  cerebeflum,  therefore,  is  intimately  connected  with  all 
sensory  centers  which  are  concerned  in  the  adjustment  of  the 
body  in  space  and  motor  control  in  general.  The  maintenance 
of  bodily  equilibrium  is  the  most  important  of  these  functions, 


THE    VESTIBULAR    APPARATUS    AND    CEREBELLUM  187 

and  the  semicircular  canals  of  the  internal  ear  (pp.  89,  196)  are 
the  receptive  organs,  which  are  of  chief  importance  in  these  reac- 
tions. Comparative  and  embryological  studies  show  that  the 
cerebellum  was  developed  as  a  direct  outgrowth  from  the  pri- 
mary centers  for  the  semicircular  canals  in  the  medulla  oblongata 
(the  acoustico-lateral  area  of  fishes.  Fig.  43),  and  even  in  the 
human  body  root  fibers  from  the  vestibular  branch  of  the  VIII 
cranial  nerve  enter  the  cerebellum  directly.  Neurons  of  the 
second  order  also  enter  the  cerebellum  from  the  vestibular 
nucleus,  as  well  as  from  the  spinal  cord  and  from  practically  all 
of  the  somatic  sensory  centers  of  the  brain;  there  is  also  a  very 
important  path  from  the  cerebral  cortex. 

The  human  cerebellum  consists  of  a  median  lobe,  the  worm 
(vermis),  and  two  larger  cerebellar  hemispheres.  The  vermis 
receives  fibers  chiefly  from  the  somatic  sensory  centers  of  the 
brain  stem  and  spinal  cord,  and  it  alone  is  well  developed  in 
lower  vertebrates  (from  fishes  to  birds,  see  Fig.  43).  The  cere- 
bellar hemispheres  vary  in  size  in  different  mammals  in  propor- 
tion to  the  size  of  the  cerebral  cortex,  being,  therefore,  much 
larger  in  man  than  in  any  other  animal.  Their  appearance  from 
the  ventral  side  is  seen  in  Fig.  53.  The  cerebellum  is  attached 
to  the  brain  stem  by  three  stalks  or  peduncles  on  each  side,  the 
superior  peduncle  (brachium  conjunctivum),  the  middle  pe- 
duncle (brachium  pontis),  and  the  inferior  peduncle  (corpus 
restiforme). 

Figure  87  illustrates  diagrammatically  the  chief  pathwaA's 
which  enter  the  cerebellum,  and  Fig.  88  those  by  which  nervous 
impulses  leave  it.  We  cannot  here  describe  these  connections 
in  detail,  but  can  mention  a  few  only  of  their  general  features. 

The  cerebellum,  as  already  stated,  receives  afferent  impulses 
from  all  of  the  important  somatic  sensory  centers  and  also  from 
the  cerebral  cortex.  The  afferent  fibers  from  the  brain  stem 
enter  by  the  superior  and  inferior  peduncles.  The  pons  is  an 
eminence  under  the  upper  part  of  the  medulla  oblongata  (Fig. 
53)  which  contains  graj^  centers  (the  pontile  nuclei).  Fibers 
pass  into  the  pontile  nuclei  from  the  association  centers  of  the 
cerebral  cortex  by  way  of  the  cortico-pontile  tracts,  and  from  the 
motor  areas  of  the  cerebral  cortex  by  way  of  collateral  branches 
from  the  cortico-spinal  tract  as  it  passes  through  the  pons. 


188 


INTRODUCTION  TO   NEUROLOGY 


These  nervous  impulses  enter  the  cerebellar  hemispheres  from 
the  pons  by  the  middle  cerebellar  peduncles. 


Tk  olivo-cereb. 
tr.spino- 
cereb.  dors, 
^lechsig) 


t^  spino-olivaris 
tr.  cortico-spinalis' 


(cerebellum 


brachium 
conjunctivurn 

'r.  tecto-cereU 

tr.  ponto-cereh 

mesencephalon 


central 

tegmental 

tract. 


]r.  cortico- 
cerebellaris 


olivQ  inferior 
tr.sp'ino-cereb.ventr.  (Gowers) 


Fig.  87. — Diagram  of  the  chief  afferent  tracts  leading  into  the  cerebellum. 


cerebellurn 


.  dentati 


rooT  nuclei 


corpus  restiforme 


bracbium   pontis 

brachium 

conjuncTivum 

tr  cereb.-tegmenTalis 
epinali 

mesencephalon 

bro.thal. 


oliva  inferior- 


-Tr.  vubro- 
spinalis 

Tr;  cere bello- 

tegmentdis 

pontis 


Jtr.  cerebello-tegmentalis   buibi 
Fig.  88. — Diagram  of  the  chief  efferent  tracts  leading  out  of  the  cerebellum. 

Fibers  leave  the  cerebellum  by  all  three  peduncles  for  the 
motor  centers  of  the  brain  stem  (the  cerebello-tegmental  tracts, 


THE    VESTIBULAR    APPARATUS    AND    CEREBELLUM  189 

Fig.  88),  and  a  much  larger  number  leave  by  the  superior  pedun- 
cle for  the  red  nucleus  (nucleus  ruber,  Fig.  75)  and  adjacent 
parts  of  the  brain  stem,  these  fibers  first  crossing  to  the  opposite 
side  of  the  brain  in  the  cerebral  peduncle  under  the  aqueduct  of 
Sylvius.  From  the  red  nucleus  fibers  pass  downward  into  the 
spinal  cord  (rubro-spinal  tract)  and  upward  to  the  cerebral 
cortex. 

The  connections  just  described  illustrate  some  of  the  pathways 
by  which  the  cerebellum  is  able  to  reinforce,  coordinate,  or 
otherwise  modify  the  somatic  motor  mechanisms.  There  is  an 
immense  amount  of  potential  nervous  energy  always  available 
in  the  neurons  of  the  cerebellar  cortex,  and  the  cerebellum  ap- 
pears to  be  constantly  exerting  a  stimulating  or  tonic  effect  upon 
the  body  muscles.  An  injury  to  the  cerebellum  (especially  an 
unsymmetric  lesion)  produces  motor  incoordination,  and  the 
total  removal  of  the  cerebellum  results  in  loss  of  muscular  tone 
and  great  weakness,  though  there  is  no  abolition  of  any  particular 
motor  functions.  The  cerebellar  cortex  and  the  cerebral  cortex 
are  very  intimately  connected  by  large  fiber  tracts,  and  each 
apparently  exerts  an  important  physiological  effect  upon  the 
other.  But  the  exact  nature  of  this  reciprocal  control  is  still 
obscure. 

The  cerebellar  cortex  differs  from  the  cerebral  cortex  in  the 
form  and  arrangement  of  its  neurons  and  also,  further,  in  that 
it  is  structurally  similar  throughout  its  entire  extent.  The 
cerebral  cortex,  on  the  other  hand,  shows  differences  in  the  forms 
and  arrangements  of  its  neurons  in  different  regions,  and  this 
is  correlated  with  a  regional  localization  of  diverse  functions 
(pp.  273,  281).  There  is  some  evidence  that  different  parts 
of  the  cerebellar  cortex  exert  a  dominant  regulatory  influence 
over  particular  large  groups  of  muscles;  but  this  localization  of 
function  is  of  a  very  general  sort  and  is  by  no  means  so  precise 
as  the  localization  of  voluntary  motor  centers  in  the  cerebral 
cortex.  Moreover,  the  physiological  influence  of  the  cerebellum 
upon  movement  is  of  a  very  different  sort  from  that  of  the  cere- 
bral cortex. 

The  surface  of  the  cerebellum  is  divided  by  deep  flssures  or 
sulci  into  narrow  leaf-like  subdivisions  termed  folia  or  gyri, 
so  that  when  it  is  cut  open  across  the  median  plane  the  cut  sur- 


190 


INTRODUCTION  TO   NEUROLOGY 


face  looks  somewhat  like  a  sprig  of  the  common  evergreen  cedar 
tree  known  as  arbor  vitae.  Hence  this  cut  surface  by  the  an- 
cients was  termed  the  arbor  vitse. 


Fig.  89. — Semidiagrammatic  section  taken  transversely  through  a 
lamina  of  the  cerebellar  cortex  (Golgi  method) :  A ,  Molecular  layer, 
filled  with  axons  of  granule  cells  cut  at  right  angles  to  their  course;  B, 
granular  layer;  C,  white  matter;  a,  Purkinje  cell,  with  the  dendrite  broadly 
spread  out  in  the  transverse  plane  (compare  Fig.  15);  b,  basket  cell  (com- 
pare Fig.  16) ;  d,  terminal  arborizations  of  the  basket  cells  enveloping  the 
bodies  of  the  Purkinje  cells;  e,  superficial  stellate  cells;/,  Golgi  cell  of  type 
II  (see  p.  43);  g,  granule  cells  with  their  axons  ascending  and  bifm-cating 
in  the  molecular  layer  at  i;  h,  mossy  fibers;  j,  neurogha  cell;  m,  neu- 
rogha  cell;  n,  cHmbing  fibers.     (After  Ramon  y  Cajal.) 


The  gray  matter  of  the  cerebellum  is  partly  superficial  (this 
is  the  cortex  to  which  reference  has  already  been  made)  and 
partly  in  the  form  of  deep  nuclei  embedded  within  the  white 
matter.     The  largest  of  these  deep  gray  centers  are  the  dentate 


THE    VESTIBULAR    APPARATUS    AND    CEREBELLUM  191 

nuclei  within  the  cerebellar  hemispheres.  Within  the  vermis 
are  other  smaller  centers,  called  the  roof  nuclei,  because  they  lie 
immediately  above  the  fourth  ventricle  (nuclei  emboliformis, 
globosus,  and  fastigii,  see  Fig.  96).  Some  of  the  afferent  fibers 
which  enter  the  cerebellum  end  in  these  nuclei,  but  most  of  them 
end  in  the  cortex.  The  efferent  fibers,  on  the  other  hand,  arise 
from  the  deep  nuclei,  especially  the  dentate  nuclei  (Fig.  88). 

The  cerebellar  cortex  has  three  distinct  layers.  External  to 
the  central  white  matter  (Fig.  89,  C)  is  a  wide  layer  composed  of 
very  minute  granule  cells  (Fig.  89,  B)  densely  crowded  together, 
with  scanty  cytoplasm,  short,  claw-like  dendrites,  and  slender 
unmyelinated  axons  which  ascend  to  the  superficial  molecular 
layer  (Fig.  89,  A),  where  they  bifurcate  (their  branches  running 
lengthwise  of  the  folium)  and  end  among  the  dendrites  of  the 
Purkinje  cells,  to  be  described  immediately.  The  middle  layer 
of  the  cortex  is  composed  of  a  single  row  of  Purkinje  cells  (Fig. 
89,  a);  these  have  large  globose  bodies  with  massive  bushy 
dendrites  directed  outward  and  slender  axons  directed  inward. 
These  axons  are  myelinated  and  constitute  the  chief  efferent 
pathway  from  the  cortex;  they  do  not,  however,  leave  the  cere- 
bellum, but  end  in  the  deep  gray  nuclei  (chiefly  the  dentate 
nuclei),  from  which  other  neurons  carry  the  impulses  out  of  the 
cerebellum.  The  dendrites  of  the  Purkinje  cells  are  widely  ex- 
panded transversely  to  the  length  of  the  folium,  but  are  very 
narrow  in  the  opposite  direction;  thus  each  cell  comes  into 
contact  with  the  largest  possible  number  of  axons  of  the 
granule  cells  which  run  lengthwise  of  the  folium.  The  outer- 
most or  molecular  layer  contains  the  dendrites  of  the  Purkinje 
cells,  termini  of  the  axons  of  the  granule  cells  and  of  other 
fibers,  and  a  small  number  of  neurons  with  short  axons,  among 
which  are  the  basket  cells  illustrated  in  Figs.  16  and  89,  h. 

Afferent  fibers  terminate  in  the  cerebellar  cortex  in  two  waj'S. 
They  may  pass  directly  out  to  the  molecular  layer  as  ascending 
or  climbing  fibers,  where  they  end  in  very  intimate  relation  with 
the  dendrites  of  the  Purkinje  cells  (Figs.  15  and  89,  n),  or  they 
may  end  as  moss  fibers  (Fig.  89,  h)  among  the  cells  of  the  gran- 
ule layer.  Here  the  granules  take  up  the  nervous  impulses  and 
deliver  them  to  the  dendrites  of  the  Purkinje  cells.  Ramon 
y  Cajal  is  of  the  opinion  that  the  moss  fibers  are  the  terminals 


192  INTRODUCTION  TO  NEUROLOGY 

of  the  afferent  fibers  of  the  inferior  cerebellar  peduncle,  and  that 
the  ascending  fibers  are  the  terminals  of  the  fibers  from  the 
middle  peduncle  (brachium  pontis). 

Since  each  fiber  from  the  inferior  peduncle  branches  exten- 
sively and  reaches  many  granule  cells  in  widely  separated  parts 
of  the  cerebellum,  and  since  the  axon  of  each  granule  cell  reaches 
the  dendrites  of  a  very  large  number  of  Purkinje  cells,  a  single 
incoming  nervous  impulse  may  excite  a  very  large  number  of 
Purkinje  cells,  and  thus  its  physiological  effect  may  be  greatly 
enhanced.  The  same  result  is  also  secured  by  the  action  of  the 
basket  cells  (Fig.  89,  6)  and  other  forms  of  neurons  with  short 
axons  within  the  cortex  (Fig.  89,  e,  /),  each  of  which  may 
discharge  powerful  impulses  directly  upon  several  Purkinje 
cells.  The  axons  of  the  Purkinje  cells  themselves  also  give  off 
collateral  fibers  into  the  granular  layer,  whose  neurons  dis- 
charge back  into  the  Purkinje  cells  again.  In  all  of  these 
ways  provision  is  made  for  the  diffusion,  summation,  and  re- 
inforcement of  stimuh  during  the  process  of  their  transmission 
through  the  cerebellar  cortex,  and  also  for  prolongation  of  motor 
reactions  which  would  otherwise  soon  subside,  and  for  the  main- 
tenance of  muscular  tone. 

This  type  of  reaction  has  been  termed  "avalanche  conduction" 
(see  p.  101),  and  its  mechanism  here  is  similar  to  that  found  in 
the  olfactory  bulb  (p.  218),  but  much  more  complex.  It  is  prob- 
able that  the  reciprocal  relation  between  the  cerebellum  and  the 
cerebral  cortex  is  of  a  similar  sort,  all  cortical  activities  exciting 
also  the  cerebellum  and  drawing  therefrom  additional  nervous 
energy  as  needed  to  maintain  the  tone  of  the  reacting  mech- 
anism; and  voluntary  movements  excited  by  the  cortico-spinal 
or  pyramidal  tract  from  the  cerebral  cortex  (see  p.  283)  are 
under  especially  direct  proprioceptive  control  from  this  source. 

The  relationships  of  the  centers  of  the  brain  stem,  the  cerebral 
cortex,  and  the  cerebellum  may  be  illustrated  somewhat  crudely 
by  the  analogy  of  the  three  chief  departments  of  the  national 
government.  The  reflex  centers  of  the  brain  stem  correspond 
to  the  legislative  branch  of  government,  determining  in  advance 
by  virtue  of  their  innate  structure  what  actions  may  appropri- 
ately be  performed  in  each  particular  type  of  frequently  recur- 
ring situation.     The  cerebral  cortex  is  a  sort  of  glorified  judicial 


THE    VESTIBULAR    APPARATUS    AND    CEREBELLUM  193 

branch  of  government,  interpreting  the  decrees  of  the  legislative 
centers,  integrating  the  behavior  by  combining  its  elements  into 
cooperating  systems  in  view  of  all  the  factors  of  present  and 
past  experience,  and  with  extensive  powers  of  veto  over  inap- 
propriate reactions  which  may  have  been  inaugurated  by  the 
lower  centers.  The  cerebellum  is  the  great  administrative 
office  which  attends  to  the  details  of  the  proper  execution  of  the 
acts  which  have  been  previously  determined  upon  and  initiated 
in  the  other  departments  of  government. 

Summary. — The  vestibular  apparatus  and  the  cerebellum  are 
genetically  and  physiologically  very  closely  related.  The  semi- 
circular canals  are  the  most  highly  differentiated  proprioceptive 
end-organs,  serving  chiefly  the  functions  of  equilibration  and 
the  maintenance  of  muscular  tone.  These  reactions  are,  for  the 
most  part,  unconsciously  performed  and  there  is  no  important 
cortical  path  from  the  vestibular  nuclei.  These  nuclei  effect 
reflex  connections  with  the  motor  centers  of  the  spinal  cord  and 
medulla  oblongata,  especially  the  eye-muscle  nuclei,  and  with  the 
cerebellum. 

The  cerebellum  has  been  developed  out  of  the  primary  vestibu- 
lar area  for  the  more  perfect  coordination  and  integration  of  the 
somatic  motor  reactions  and  for  strengthening  these  reactions. 
It  receives  afferent  fibers  from  all  somatic  sensory  centers,  and 
in  mammals  it  is  also  very  intimately  connected  with  the  cere- 
bral cortex,  these  two  higher  centers  appearing  always  to  act 
conjointly.  The  cerebellum  discharges  into  all  of  the  somatic 
motor  centers  and  assists  in  preserving  the  proper  balance  of 
muscular  contraction  and  in  the  maintenance  of  muscular  tone. 


LiTEBATURE 

For  the  original  sources  of  the  data  presented  in  this  and  the  preceding 
chapters  see  the  bibhographies  appended  to  Chapters  VII,  VIII,  IX,  and  X. 
On  the  cerebellum  see  further : 

Andre-Thomas  and  Durupt,  A.  1914.  Localisations  cer^beUeuses, 
Paris. 

BiANCHi,  A.  1903.  Sulle  vie  di  connessione  del  cervelletto,  Arch,  di 
Anat.  e  EmbrioL,  vol.  ii. 

BoLK,  L.  1906.  Das  Cerebellum  der  Saiigethiere,  Jena. 

Bruce,  A.  N.  1910.  The  Tract  of  Gowers,  Quart.  Jour.  Exp.  Physiol., 
vol.  iii,  pp.  391-407. 

13 


194  INTRODUCTION  TO  NEUROLOGY 

Ferrier,  D.,  and  Turner,  W.  A.  1895.  A  Record  of  Experiments  Illus- 
trative of  the  Symptomatology  and  Degenerations  Following  Lesions  of  the 
Cerebellum,  Phil.  Trans.  Roy.  Soc.  London  for  1894,  vol.  clxxxv  B,  pp. 
755-761. 

Gehtjchten,  a.  Van.  1904.  Le  corps  restiforme  et  les  connexions 
bulbo-cerebelleuses,  Le  Nevraxe,  vol.  vi. 

— .  1905.  Les  pedoncules  cerebelleuses  superieurs,  Le  Nevraxe,  vol.  vii. 

Goldstein,  K.  1910.  Ueber  die  aufsteigende  Degeneration  und  Quer- 
schnittsunterbrechung  des  Rtickenmarks  (Tractus  spino-cerebellaris  pos- 
terior, Tractus  spino-ohvaris,  Tractus  spino-thalamicus),  Neurol.  Central- 
blatt,  No.  17. 

Herrick,  C.  Judson.  1914.  The  Cerebellum  of  Necturus  and  Other 
Urodele  Amphibia,  Jour.  Comp.  Neur.,  vol.  xxiv,  pp.  1-29. 

Herrick,  C.  L.  1891.  Illustrations  of  the  Architectonic  of  the  Cere- 
bellum, Jour.  Comp.  Neur.,  vol.  i,  pp.  5-14. 

Lewandowsky,  M.  1907.  Die  Funktionen  des  zentralen  Nervensys- 
tems,  Jena. 

LuciANi,  L.  1893.  Das  Kleinhirn,  Leipzig. 

Russell,  J.  S.  Riesen.  1895.  Experimental  Researches  into  the  Func- 
tions of  the  Cerebellum,  Phil.  Trans.  Roy.  Soc.  London,  vol.  clxxxv  B, 
pp.  819-861. 

ScHAPER,  A.  1894.  Die  morphologische  und  histologische  Entwickelung 
des  Kleinhirns  der  Teleostier,  Morph.  Jahrb.,  Bd.  xxi. 

Sherrington,  C.  S.  1909.  On  Plastic  Tonus  and  Proprioceptive  Re- 
flexes, Quart.  Jour.  Exp.  Physiol.,  vol.  ii,  p.  109. 

Wilson,  J.  Gordon,  and  Pike,  F.  H.  1912.  The  Effects  of  Stimulation 
and  Extirpation  of  the  Labyrinth  of  the  Ear,  and  Their  Relation  to  the 
Motor  System,  Phil.  Trans.  Roy.  Soc.  London,  vol.  cciii  B,  pp.  127-160. 


CHAPTER  XIII 

THE   AUDITORY   APPARATUS 

The  human  organ  of  hearing  consists  of  the  external  ear, 
bounded  within  by  the  drum  membrane  (tympanic  membrane, 
membrana  tympani);  the  middle  ear,  a  cavity  filled  with  air 
which  communicates  with  the  pharynx  through  the  auditory 


Tympanic  cavity,  with  chain  of  ossicles 
Semicircular  duct 
Utricle 


Ductus  endolymphaticus 
Saccule 
Ductus  cochlearis 


Auricula 


Auditory  tube 

Membrana  tympani 

Recessus  epitjrmpanicus 

External  acoustic  meatus 


Fig.  90. — Diagrammatic  view  of  the  parts  of  the  human  ear. 
Cunningham's  Anatomy.) 


(From 


or  Eustachean  tube  and  contains  the  auditory  ossicles;  and  the 
internal  ear,  a  complex  bony  chamber,  the  bony  labyrinth, 
within  which  is  the  membranous  labyrinth  containing  the  specific 
receptors  or  sensory  surfaces  of  the  internal  ear  (Fig.  90).     The 

195 


196 


INTRODUCTION   TO   NEUROLOGY 


tympanic  membrane  receives  the  air  waves  which  form  the 
physical  stimuli  of  sound  (pp.  70  and  85).  These  vibrations  are 
then  transmitted  (and  at  the  same  time  intensified)  by  the  au- 
ditory ossicles  of  the  middle  ear  to  the  liquid  within  the  bony 
labyrinth. 

The  membranous  labyrinth  is  of  approximately  the  same  shape 
as  the  bony  labyrinth,  but  smaller,  so  that  there  is  a  space  be- 
tween the  membranous  labyrinth  and  the  enclosing  bony  wall. 
This  space  is  filled  with  liquid,  the  perilymph,  and  the  mem- 
branous labyrinth  is  also  filled  with  liquid,  the  endolymph.  In 
Fig.  90  the  perilymphatic  space  is  printed  in  black  and  the  endo- 
lymphatic space  in  white.  The  parts  of  the  membranous  laby- 
rinth are  shown  diagrammatically  in  Fig.  91. 


Recessus  utriculi 
Saccule    | 


■Ampulla  of  superior  semi- 
circular duct 
Ampulla  of  lateral  duct 


Ductus  cochlearisA 
Ductus  reuniena 
Ductus  endolymphaticus 


Ampulla  of  posterior  duct 
Saccus  endolymphaticus 


Cms  commune 

Ductus  utriculosaecularis 

Sinus  inferior 


Fig.  91. — Diagrammatic  representation  of  the  parts  of  the  membranous 
labyrinth.     (From  Cunningham's  Anatomy.) 


The  membranous  labyrinth  is  a  closed  sac  which  has  four  chief 
parts:  (1)  the  utricle  (recessus  utriculi),  with  a  patch  of  sensory 
epithelium,  the  macula  utriculi;  (2)  the  three  semicircular  canals 
(ductus  semicirculares),  each  of  which  communicates  at  both 
ends  with  the  utricle  and  has  at  one  end  a  dilation  (ampulla) 
containing  a  patch  of  sensory  epithelium,  the  crista;  (3)  the 
saccule  (sacculus)  connected  by  a  narrow  ductus  utriculosaecu- 
laris with  the  utricle  and  containing  a  patch  of  sensory  epithe- 
lium, the  macula  sacculi;  (4)  the  ductus  cochlearis,  which  com- 
municates by  a  narrow  ductus  reuniens  with  the  saccule  and  is 
spirally  wound  to  fit  the  bony  cochlea,  which  is  shaped  like  a  snail 
shell.     The  ductus  cochlearis  (old  name,  scala  media)  is  trian- 


THE    AUDITORY    APPARATUS 


197 


gular  in  cross-section  (Fig.  92)  and  contains  the  specific  auditory 
receptive  epithelium  in  the  spiral  organ,  or  organ  of  Corti. 


Membrana  tectoria 


Cochlear , 
nerve- 
fibers 


fScaJa  Tympan! 

Inner  hair  cell 


Membrana  basilans 
Outer  hair  cells 


Fig.  92. — Section  across  the  ductus  cochlearis  (scala  media)  to  illustrate 
the  relations  of  the  spiral  organ  (organ  of  Corti).     (After  Retzius.) 


Inner  rod  of  Corti 


Inner  hair  cell 
Hensen'a  stripe 
Membrana  tectoria 
Sulcus  spiralis  intemus 
Limbus  laminae  spiralis 


Outer  rod  of  Corti 
Outer  hair  cells 

Cells  of  Hensen 

Membrana  basilans 


Cells  of  Claudius 


Branches-     ^ 
of  cochlear       "—S- 


Inner  spiral  fasciculus 

Vas  spirale 
Tunnel  of  Corti 


Cells  of  Deiters 


Space  of  Nuel 

Fig.  93. — Section  across  the  spiral  organ  (organ  of  Corti)  from  the  central 
coil  of  the  ductus  cochlearis.     (After  Retzius.) 


The  generally  accepted  structure  of  the  spiral  organ,  as  presented  in 
the  classical  researches  of  Retzius,  is  shown  in  Fig.  93.  Upon  a  basement 
membrane  (Fig.  92,  membrana  basilaris)  is  a  very  highly  differentiated 


198 


INTRODUCTION   TO    NEUROLOGY 


sensory  epithelium,  part  of  whose  cells  are  supporting  elements  of  diverse 
sorts  and  part  (the  hair  cells)  are  specific  receptors.  The  termini  of  the 
cochlear  nerve  arborize  around  the  bodies  of  the  hair  cells  in  the  same  way 
that  fibers  of  the  vestibular  nerve  are  related  to  the  hair  cells  of  the  cristse 
of  the  semicircular  canals  (Fig.  32,  p.  88).  The  membrana  tectoria  is 
a  delicate  gelatinous  mass  resting  upon  the  spiral  organ  and  intimately 
connected  with  the  hairs  of  the  hair  cells.  Its  shape  has  been  very  care- 
fully studied  by  Hardesty. 

Many  details  of  the  structure  of  the  spiral  organ,  or  organ  of  Corti,  and 
the  whole  question  of  the  mode  of  its  functioning  are  still  controverted. 
Our  present  knowledge  of  the  histological  organization  of  the  basilar  mem- 
brane shows  that  it  is  structurally  incapable  of  serving  the  function  of  tone 
analysis  in  the  way  postulated  by  Helmholtz's  theory.  Based  upon  im- 
portant additions  to  our  knowledge  of  the  minute  structure  of  the  organ 


ri.coc 


Fig.  94. — Section  through  the  apical  turn  of  the  cochlea  of  the  pig  at 
about  full  term,  showing  outer  auditory  hairs  embedded  in  the  membrana 
tectoria:  ep.s.sp.,  Epithelium  of  spiral  sulcus;  i.h.c,  inner  hair  cells;  i.pil., 
inner  pillar;  m.bas.,  basement  membrane;  ni.teci.,  membrana  tectoria;  lab. 
vest.,  labium  vestibulare;  n.coch.,  cochlear  nerve;  o.h.c,  outer  hair  cell;  s.sp., 
sulcus  spirahs.     (After  C.  W.  Prentiss.) 


of  Corti  and  chnical  observations  upon  diseased  conditions,  several  different 
theories  of  the  mechanism  of  tone  analysis  have  recently  been  expressed. 
Anaong  the  more  important  of  these  researches  are  those  of  Shambaugh. 
This  author  has  demonstrated  that  the  hairs  of  the  hair  cells  do  not  termi- 
nate freely  in  the  endolymph,  as  commonly  figured,  but  that  they  are 
firmly  attached  to  the  under  surface  of  the  tectorial  membrane.  This 
membrane  has  a  semigelatinous  texture  and  is  capable  of  taking  up  sym- 
pathetically the  vibrations  of  the  endolymph  within  which  it  floats. 

The  development  of  the  tectorial  membrane  has  recently  been  restudied  by 
Prentiss  and  Hardesty.  It  first  appears  as  a  thin  cuticular  plate  developed 
over  the  free  ends  of  the  columnar  cells  which  form  the  inner  or  axial  part  of 
the  epithelium  of  the  basement  membrane.  In  the  adult  ear  it  retains  its 
attachment  to  the  labium  vestibulare  along  the  axial  border  of  the  ductus 
cochlearis,  but  becomes  free  from  the  cells  which  form  the  lining  of  the 


THE    AUDITORY    APPARATUS  199 

sulcus  spiralis  (Fig.  94).  Prentiss  claims  that  it  is  in  part  formed  from  the 
embryonic  cells  which  develop  into  the  spiral  organ,  and  that  its  connection 
with  the  spiral  organ  is  retained  in  the  adult  (Fig.  94);  but  Hardesty  (1915) 
says  that  the  cells  of  the  embryonic  spiral  organ  contribute  httle  or  nothing 
to  the  formation  of  the  tectorial  membrane  and  that  this  membrane  is  free 
from  the  spiral  organ  in  the  adult.  Prentiss  describes  the  membrane  as 
growing  in  thickness  by  the  secretion  of  a  cuticulum  formed  between  the 
ends  of  the  epithelial  cells,  thus  giving  to  the  mature  membrane  a  cham- 
bered or  honey-comb  structure.  Hardesty,  however,  regards  it  as  produced 
by  fibrils  growing  out  from  the  free  ends  of  the  epithelial  cells  lying  be- 
tween the  embryonic  spiral  organ  and  the  axis  of  the  cochlea,  these  fibrils 
being  embedded  in  a  gelatinous  matrix. 

Shambaugh  concludes  that  the  tectorial  membrane  takes  the  part  of  a 
physical  resonator  by  responding  in  its  various  parts  to  tones  of  different 
pitch,  depending  on  the  size  of  the  membrane,  tones  of  higher  pitch  being 
taken  up  by  the  hair  cells  located  near  the  beginning  of  the  basal  coil,  those 
of  lower  pitch  by  the  cells  near  the  apex  of  the  cochlea,  where  the  tectorial 
membrane  attains  its  maximum  size.  The  stimulation  of  the  hair  cells  is 
effected  only  through  the  medium  of  their  projecting  hairs,  these  being 
excited  by  vibrations  of  the  tectorial  membrane  to  which  they  are  attached. 

In  fishes  the  organs  of  the  internal  ear  are  intimately  associated  with  an 
extensive  series  of  subcutaneous  canals  containing  numerous  sense  organs 
and  with  naked  cutaneous  sense  organs  of  the  same  type,  the  entire  complex 
forming  the  system  of  lateral  line  sense  organs  (see  p.  110  and  Fig.  95). 
The  nerves  which  in  fishes  supply  the  lateral  line  sense  organs  (lateralis 
roots  of  the  VII  and  X  cranial  nerves)  and  the  organs  of  the  internal 
ear  (VIII  nerve)  are  intimately  associated  and  terminate  together  in  the 
acoustico-lateral  area  of  the  medulla  oblongata  (Figs.  43.  and  44,  pp.  Ill, 
112),  and  all  of  these  end-organs  have  the  same  type  of  structure  as  those 
of  the  human  internal  ear  (Fig.  32,  p.  88). 

The  internal  ears  of  fishes  are  essentially  similar  to  those  of  man  save 
that  they  lack  the  cochlea  and  the  organ  of  Corti.  They  possess  a  small 
sense  organ  in  the  saccule,  the  lagena,  supplied  by  a  special  branch  of  the 
VIII  nerve  (Fig.  95,  RL),  from  which  the  cochlea  of  higher  vertebrates  has 
been  developed.  The  researches  of  Parker  have  shown  that  fishes  hear, 
though  there  is  no  evidence  that  they  possess  the  power  of  tone  analysis, 
and  the  sense  organs  of  the  saccule  are  the  essential  receptors  for  sound 
waves.  ■  The  sense  organs  of  the  lateral  line  system  are  said  by  Parker  to  be 
sensitive  to  water  vibrations  of  slower  frequency  than  the  sound  waves  to 
which  the  ear  responds,  while  Hofer  is  of  the  opinion  that  these  organs  are 
stimulated  only  by  streaming  movements  of  the  water  in  which  the  animals 
live.  Probably  the  lateral  line  organs  also  participate  in  the  equihbratory 
reactions  of  the  fish. 

Though  our  knowledge  of  the  functions  of  the  various  parts  of  the  acous- 
tico-lateral system  of  fishes  is  still  very  imperfect,  it  is  evident  that  all  of 
these  organs  are  both  structurally  and  physiologically  of  common  type,  and 
it  is  probable  that  they  have  had  a  common  evolutionary  origin  from  a  more 
generahzed  form  of  cutaneous  tactile  organ.  This  is  the  explanation  of  the 
intimate  association  in  the  human  ear  of  sense  organs  of  so  diverse  fimctions 
as  the  cochlea  for  hearing  and  the  semicircular  canals  for  equilibration,  the 
former  being  an  exteroceptor  whose  reactions  may  be  vividly  conscious,  and 
the  latter  being  a  proprioceptor  whose  reactions  are  almost  entirely  uncon- 
sciously performed.  For  further  consideration  of  the  semicircular  canals 
and  their  central  connections  see  p.  183. 


200 


INTRODUCTION  TO   NEUROLOGY 


In  the  human  body  the  cochlear  and  vestibular  nerves  are 
very  intimately  associated,  but  the  embryological  studies  of 


Fig.  95. — Diagram  of  the  acoustico-lateral  system  of  nerves  with  their 
peripheral  end-organs,  as  seen  from  the  right  side,  in  a  fish,  the  common 
silver-sides,  Menidia  (X  9).  The  relations  here  figured  were  recon- 
structed from  serial  sections  by  projection  upon  the  sagittal  plane.  For 
the  relations  between  the  acoustico-lateral  nerves  and  the  other  systems 
of  nerves  in  this  fish,  see  the  more  detailed  chart  from  which  this  was  drawn 
off,  in  the  Journal  of  Comparative  Neurology,  vol.  ix,  1899,  plate  15;  cf. 
also  Fig.  65,  p.  149,  of  this  book.  The  dotted  outline  represents  the  posi- 
tion of  the  brain,  the  lateral  line  canals  are  shaded  with  cross-hatching,  the 
internal  ear  is  stippled,  and  the  nerves  are  drawn  in  black.  The  organs 
of  the  lateral  fine  system  are  drawn  as  black  disks  when  naked  on  the 
surface  of  the  skin,  and  as  black  circles  when  lying  in  the  canals.  NAA, 
Anterior  nasal  aperture;  NAP,  posterior  nasal  aperture;  N  OL,  olfactory 
nerve;  N  OPT,  optic  nerve;  RAA,  nerve  of  superior  ampulla;  RAE,  nerve 
of  lateral  ampulla;  RAP,  nerve  of  inferior  ampulla;  R  BUG,  ramus  bucca- 
lis  of  facial  nerve;  RL,  nerve  of  the  lagena  (rudimentary  spiral  organ); 
RLAT,  ramus  laterahs  of  the  vagus;  ROS,  ramus  ophthalmicus  super- 
ficiahs  of  the  facial  nerve;  R  MAN  EX,  ramus  mandibularis  extemus  of 
the  facial  nerve;  R  SAC,  nerve  of  the  sacculus;  RU,  nerve  of  the  utriculus; 
T,  acoustico-lateral  area.  (After  Herrick,  from  Wood's  Reference  Hand- 
book of  the  Medical  Sciences.) 

Streeter  and  others  have  made  it  plain  that  these  two  nerves  are 
really  more  distinct  than  was  formerly  supposed.     The  periph- 


THE    AUDITORY    APPARATUS 


201 


eral  receptors  of  the  cochlea  and  semicircular  canals  are  obviously 
as  dissimilar  as  are  their  functions,  but  the  functional  significance 


Inferior  quadrigeminate  body 


^5?>l^■'■^       _^Nucleus  of  trochlear  nerve 


Nucleus  fastigii 

Nucleus  emboUformis 


Dentate  nucleus 


Lateral  nucleus  o( 

'  '  vestibular  nerve 

_,Restiform  body 

Dorsal  nucleus  ot 

cochlear  nerve 

^,Ventral  nucleus  of 

cochlear  nerve 
^.•Cochlear  nerve 


Nucleus  of  lateral  lemniscus 

Medial  longitudinal  fasciculus 

Lateral  lemniscus. 

Peduncle  of  superior  oUve^ 


Vestibular  nerve 
Superior  Olivary  nucleus 
Trapezoid  body 

Fig.  96. — Diagram  of  the  auditory  and  vestibular  connections.  Com- 
pare Figs.  71,  77,  and  86.  The  fibers  of  the  cochlear  nerve  enter  the  ven- 
tral and  dorsal  cochlear  nuclei  (the  latter  being  termed  the  tuberculum 
acusticum)  at  the  lateral  border  of  the  medulla  oblongata.  The  auditory 
path  now  divides,  one  tract,  the  trapezoid  body,  passing  ventrally  through 
the  pons  to  enter  the  lateral  lemniscus  of  the  opposite  side,  and  the  other 
passing  dorsally  through  the  acoustic  medullary  strise  (striae  meduUares 
acustici)  across  the  floor  of  the  fourth  ventricle  and  also  entering  the  lat- 
eral lemniscus.  These  fibers  may  be  interrupted  by  synapses  in  the  supe- 
rior olives,  the  nucleus  of  the  lateral  lemniscus  or  the  inferior  colliculus 
(inferior  quadrigeminate  body)  before  they  reach  the  medial  geniculate 
body  of  the  thalamus,  or  they  may  pass  by  these  nuclei  without  connecting 
with  them.  The  fibers  shown  in  the  diagram  as  passing  from  the  inferior 
quadrigeminate  body  to  the  temporal  lobe  of  the  cerebral  cortex  are  prob- 
ably interrupted  by  a  synapse  in  the  medial  geniculate  body.  (From 
Morris'  Anatomy.) 


of  the  sensor}'-  organs  of  the  utricle  and  saccule  is  more  uncertain. 
The  fact  that  fishes  undoubtedly  hear,  notwithstanding  their 
lack  of  cochlea  or  any  other  receptors  more  complex  than  the 


202  INTRODUCTION  TO  NEUROLOGY 

sensory  spots  in  the  saccule,  demonstrates  the  relatively  late 
phylogenetic  origin  of  the  cochlear  system  from  the  vestibular, 
and  has  suggested  to  some  physiologists  that  even  in  man  these 
two  systems  are  not  wholly  distinct,  and  that  the  sense  organs  in 
the  saccule  may  also  function  as  a  sound  receptor.  It  is  clear, 
however,  that  tone  analysis  is  effected  only  in  the  cochlea. 

The  central  connections  of  the  cochlear  and  vestibular  nerves 
are  fundamentally  different.  The  vestibular  nerve  terminates 
in  reflex  centers  of  the  medulla  oblongata  and  cerebellum  (p. 
185)  with  no  important  cortical  connections,  while  the  cochlear 
nerve  has,  in  addition  to  important  reflex  connections  in  the  ob- 
longata and  midbrain,  the  much  stronger  ascending  pathway  of 
the  lateral  lemniscus  directly  to  the  medial  geniculate  body  of 
the  thalamus,  and  thence  to  the  temporal  lobe  of  the  cerebral 
cortex  (see  p.  157  and  Figs.  75,  77,  80,  96).  Some  of  the  fibers 
of  the  lateral  lemniscus  are  interrupted  in  the  inferior  colliculus, 
which  is  an  important  auditory  reflex  center. 

Summary. — The  human  ear  has  three  parts:  (1)  the  external 
ear,  for  receiving  sound  waves  from  the  air;  (2)  the  middle  ear, 
for  intensifying  the  vibrations  and  transmitting  them  to  (3)  the 
internal  ear,  which  is  filled  with  liquid  and  contains  sense  organs 
of  uncertain  function  in  the  utricle  and  saccule,  sense  organs  for 
equilibration  in  the  semicircular  canals,  and  the  spiral  organ 
(organ  of  Corti)  in  the  cochlea  for  tone  analysis.  The  spiral 
organ  is  a  complicated  epithelial  structure  resting  on  a  basement 
membrane  and  consisting  of  supporting  cells  of  diverse  kinds, 
the  hair  cells  (which  are  the  specific  receptors  and  receive  the 
endings  of  the  fibers  of  the  cochlear  nerve),  and  the  tectorial  mem- 
brane. Shambaugh  is  of  the  opinion  that  the  tectorial  membrane 
is  capable  of  responding  in  its  various  parts  to  different  vibration 
frequencies,  and  that  the  hair  cells  are  stimulated  through  their 
hairs  which  are  attached  to  the  tectorial  membrane. 

In  fishes  the  organ  of  hearing  is  much  simpler  than  in  man,  the 
semicircular  canals  are,  however,  similar,  and  there  iS,  in  addi- 
tion, an  elaborate  system  of  lateral  line  sense  organs  whose  func- 
tions seem  to  be  intermediate  between  the  tactile  and  auditory 
organs.  It  is  probable  that  these  three  systems  of  sense  organs 
were  derived  phylogenetically  from  some  more  generalized  form 
of  cutaneous  tactile  organ.     This  accounts  for  the  intimate  as- 


THE    AUDITORY    APPARATUS  203 

sociation  in  the  human  ear  of  organs  of  so  diverse  functions  as  the 
semicircular  canals  and  the  cochlea. 

The  central  connections  of  the  vestibular  and  cochlear  nerves 
are  very  different,  the  former  effecting  chiefly  reflex  connections 
for  equilibration  in  the  medulla  oblongata  and  cerebellum,  and 
the  latter  both  reflex  connections  in  the  brain  stem  and  cortical 
connections  through  the  lateral  lemniscus,  medial  geniculate 
body  of  the  thalamus  and  auditory  radiations,  for  conscious 
sensations  of  hearing. 

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organ  des  Nervus  octavus,  Wiesbaden,  J.  F.  Bergmann. 

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rinth and  the  Acoustic  and  Facial  Nerves  in  the  Human  Embryo,  Amer. 
Jour.  Anat.,  vol.  vi. 

Watson,  J.  B.  1914.  Behavior,  An  Introduction  to  Comparative  Psy- 
chology, New  York,  Chapter  XII. 


CHAPTER  XIV 

THE   VISUAL   APPARATUS 

The  eye  is  the  most  highly  specialized  sense  organ  in  the 
human  body,  and  in  other  respects  it  occupies  a  very  unique 
position.  The  essential  receptive  part  of  the  eye  is  in  the  retina. 
But  the  retina  is  much  more  than  this;  it  is  really  a  part  of  the 
brain,  and  the  so-called  optic  nerve  is  a  true  cerebral  tract.  This 
is  evident  from  a  consideration  of  the  embryologic  development 
of  the  retina. 

In  the  early  embryonic  stages  the  neural  tube  expands  laterally  in  the 
position  of  the  future  thalamus,  and  from  the  upper  part  of  this  region  a 
"primary  optic  vesicle"  is  evaginated  from  the  lateral  wall  on  each  side 

Optic  cup 
Optic  stalk   1  Lens  rudiment 


Cavity  of  forebrain  .^ 


Ectoderm  forming  lens 
rudiment 


Optic  vesicle  becoming 
cupped 

Fig.  97. — Diagrammatic  section  through  the  head  of  a  fetal  rabbit  to 
illustrate  the  mode  of  formation  of  the  primary  and  secondary  optic  vesicles 
and  of  the  lens  of  the  eye.  The  right  side  of  the  figure  is  drawn  from  a  more 
advanced  stage  than  the  left  side.     (From  Cunningham's  Anatomy.) 


(Figs.  46,  47,  49,  97).  The  optic  vesicle  grows  outward  toward  the  skin 
and  assumes  the  form  of  a  hollow  sphere,  whose  cavity  remains  in  com- 
munication with  that  of  the  third  ventricle  by  a  hollow  stalk  (Fig.  97). 
While  the  formation  of  the  primary  optic  vesicle  is  in  progress  the  overlying 
ectoderm  (outer  skin)  is  thickened  and  finally  invaginated  to  form  the  lens 
of  the  eye,  the  optic  vesicle  collapses  so  that  its  cavity  is  obliterated  by  the 
apposition  of  its  lateral  and  medial  walls,  and  a  secondary  cavity  (the  sec- 

204 


THE    VISUAL   APPARATUS  205 

ondary  optic  vesicle  or  optic  cup)  is  formed  whose  walls  are  two-layered, 
being  composed  of  both  the  original  lateral  and  medial  parts  of  the  primary 
optic  vesicle  (Fig.  97,  on  the  right  side).  This  secondary  cavity  contains 
the  vitreous  humor  in  the  adult  eye ;  the  layer  of  the  secondary  optic  vesicle 
which  borders  the  vitreous  humor  forms  the  retina;  the  outer  layer  of  the 
vesicle  forms  the  pigment  layer  of  the  retina;  and  the  stalk  forms  the  optic 
nerve  by  the  ingrowth  of  fibers  throughout  its  length  from  the  retina  and 
brain  (Fig.  100). 

The  retina,  then,  is  as  truly  a  part  of  the  brain  as  is  the  cerebral 
hemisphere  and  its  structure  is,  in  general,  similar  to  that  of 
other  parts  of  the  brain.  There  are  supporting  cells,  the  fibers 
of  Miiller  (Fig.  98,  M),  and  neuroglia  elements  (Fig.  98,  d.s.  and 
S.S.),  and  lying  among  these  are  the  neurons.  The  latter  can 
be  classified  in  general  in  four  groups:  (1)  the  rods  and  cones 
(Fig.  98,  A);  (2)  the  bipolar  cells  (Fig.  98,  D);  (3)  the  so-called 
ganglion  cells  which  give  rise  to  fibers  of  the  optic  nerve  (Fig. 
98,  F);  (4)  horizontally  disposed  correlation  neurons  (Fig.  98, 
h).  All  of  these  types  except  the  third  are  intrinsic  to  the  retina, 
i.  e.,  they  send  none  of  their  fibrous  processes  beyond  the  limits 
of  the  retina  itself.  The  axons  of  the  neurons  of  the  third  type 
pass  out  of  the  retina  and  form  the  so-called  optic  nerve,  termi- 
nating in  the  thalamus  or  midbrain. 

Immediately  external  to  the  nervous  layer  of  the  retina  is  the 
pigment  layer  (Figs.  99,  100),  which  is  formed  from  the  outer 
epithelial  layer  of  the  secondary  optic  vesicle  (Fig.  97) .  Figure 
99  illustrates  the  ten  layers  of  the  retina  as  figured  by  the  older 
histologists,  and  Fig.  98  illustrates  the  relations  of  some  of  the 
nervous  elements  as  revealed  by  the  Golgi  method.  It  is  evi- 
dent that  the  "nuclear"  or  "granular"  layers  are  characterized 
chiefly  by  the  presence  of  the  cell  bodies  of  the  neurons  and  their 
nuclei,  while  the  "molecular"  layers  are  composed  chiefly  of  the 
fibrillar  nerve-endings  which  form  the  synapses  between  the 
various  groups  of  neurons. 

The  rods  and  cones  of  the  retina  are  the  receptors  and  also 
the  neurons  of  the  first  order  in  the  optic  path.  Their  free  ends 
project  through  the  external  limiting  membrane  into  the  pigment 
layer.  Rays  of  light  which  pass  through  the  dioptric  apparatus 
(lens,  humors,  etc.)  of  the  eyeball  must  penetrate  also  the  entire 
thickness  of  the  retina  (which  is  very  transparent)  before  they 
reach  these  receptors  (Fig.  100). 


206 


INTRODUCTION   TO    NEUROLOGY 


Fig.  98. — Two  transverse  sections  through  the  mammaUan  retina:  A, 
Layer  of  rods  and  cones;  ar,  internal  arborizations  of  bipolar  neurons  related 
to  the  cones;  ar',  internal  arborizations  of  bipolar  neurons  related  to 
the  rods;  B,  outer  nuclear  layer;  C,  outer  molecular  layer;  c,  cones;  ex., 
contact  of  bipolar  neurons  with  branches  of  the  cone  fibers;  c.l.,  bi- 
polar neurons  related  to  cones;  e.g.,  cone  granules  or  nuclei  of  cones; 
c.n.,  centrifugal  nerve-fiber;  e.r.,  contact  of  bipolar  neurons  with  ends  of 
rod  fibers;  D,  inner  nuclear  layer;  d.s.,  diffuse  neurogha  elements;  E,  inner 
molecular  layer;  F,  ganglionic  layer;  G,  layer  of  nerve-fibers;  g,  neurons  of 
the  ganghonic  layer;  h,  horizontal  cells;  M,  supporting  fiber  of  Mliller; 
r,  rods;  r.b.,  bipolar  neurons  related  to  rods;  r.g.,  rod  granules  or  nuclei  of 
rods;  s.g.,  stratified  ganghon  cells;  s.s.,  stratified  neurogha  elements.  (After 
Ramon  y  Cajal.) 


THE    VISUAL    APPARATUS 


207 


The  peripheral  ends  of  the  rods  contain  a  pigment,  the  visual 
purple  or  rhodopsin,  which  is  chemically  changed  by  light  rays 
and  has  been  supposed  to  function  as  the  exciting  agent  for  ner- 
vous impulses  of  sensibility  to  light  in  the  rod  cells.  But  recent 
experiments  go  to  show  that  the  visual  purple  is  concerned  with 


stratum 
ji  /■pigmenti 


Gangli- 
onic 
layer 

stratum 
Copticum 

Membrana  limitans  interna 

Fig.  99. — Diagrammatic  section  tlirough  the  human  retina  to  illustrate 
the  ten  layers  as  commonly  enumerated.  (After  Schultze,  from  Cunning- 
ham's Anatomy.) 

the  adaptation  of  the  eye  to  different  intensities  of  light  rather 
than  with  the  specific  receptor  function  itself.  The  brown  pig- 
ment of  the  pigment  layer  is  probably  also  concerned  with  light 
adaptation. 

The  exact  mechanism  through  the  agency  of  which  the  rods 
and  cones  are  excited  to  nervous  activity  by  light  is  still  obscure; 


208 


INTRODUCTION  TO   NEUROLOGY 


but  when  the  rods  and  cones  are  once  actuated,  they  may  trans- 
mit their  nervous  impulses  across  synapses  in  the  external 
molecular  layer  to  neurons  of  the  second  order  whose  cell  bodies 
lie  in  the  internal  granular  layer.  The  neurons  of  the  internal 
granular  layer  are  of  diverse  sorts,  some  of  them  spreading  the 
nervous  impulse  laterally  (probably  for  summation  effects  in 
weak  illumination),  but  most  of  them  conducting  radially  and 
effecting  synaptic  connection  with  the  dendrites  of  the  "ganglion 
cells  of  the  retina."  The  latter  are  neurons  of  the  third  order 
whose  axons  form  the  larger  part  of  the  fibers  of  the  so-called 


Fig.  100. — Diagram  of  the  relations  of  the  retina  and  the  so-called  optic 
nerve  to  the  other  parts  of  the  brain. 


optic  nerve,  which  is  really  not  a  peripheral  nerve  at  all,  but  a 
true  cerebral  tract. 

The  fibers  of  the  "optic  nerve,"  having  reached  the  ventral 
surface  of  the  brain,  enter  the  optic  chiasma,  where  part  of  them 
cross  to  the  opposite  side  of  the  brain,  while  others  enter  the 
"optic  tract"  of  the  same  side.  From  the  chiasma  a  big  tract  of 
crossed  and  uncrossed  optic  fibers  passes  upward  and  backward 
across  the  surface  of  the  thalamus,  where  they  divide  into  two 
groups.  Some  terminate  in  the  pulvinar  and  lateral  geniculate 
body  which  form  the  postero-dorsal  part  of  the  thalamus  (Figs. 
45,  76, 77) ;  others  pass  these  structures  to  end  in  the  roof  of  the 
superior  coUiculus  of  the  midbrain,  i.  e.,  in  the  optic  tectum. 


THE    VISUAL    APPARATUS  209 

The  latter  connection  is  for  responses  of  purely  reflex  type, 
chiefly  those  concerned  with  the  movements  of  the  eyeballs  and 
accommodation  of  the  eyes;  the  thalamic  connection  is  a  station 
in  the  cortical  visual  path. 

From  these  relations  it  follows  that  there  is  nothing  in  the 
visual  organs  which  corresponds  to  a  peripheral  nerve.  The 
retina  as  a  part  of  the  brain  is  directly  excited  by  the  light  waves 
which  penetrate  its  substance.  The  so-called  optic  nerve  is  a 
tract  within  the  brain,  whose  fibers  for  the  most  part  come  from 
visual  neurons  of  the  third  order  in  the  retina,  though  there  are 
others  also  which  come  from  the  brain  and  pass  outward  to  end 
by  free  arborizations  wdthin  the  retina  (Fig.  98,  cm.).  The 
function  of  these  centrifugal  fibers  to  the  retina  is  unknown. 
Identically  the  same  nerve-fibers  w^hich  make  up  the  so-called 
optic  nerves  peripherally  of  the  optic  chiasma  are  called  the 
optic  tracts  centrally  of  that  point.  It  would  be  more  logical 
to  name  these  fibers  optic  tracts  for  their  entire  length,  these 
tracts  being  very  similar  to  those  of  the  lemniscus  system.  Like 
the  lemniscus  fibers,  they  decussate  completely  in  the  optic 
chiasma  in  lower  vertebrates  before  terminating  in  the  thalamus 
and  midbrain.  It  is  only  in  animals  with  an  overlapping  of  the 
fields  of  vision  of  the  two  eyes  and  stereoscopic  vision  that  the 
decussation  of  the  optic  tracts  in  the  chiasma  is  incomplete. 

The  significance  of  the  crossed  and  uncrossed  fibers  of  the 
optic  tracts  is  seen  in  Fig.  101.  In  this  diagram  the  shaded  por- 
tions of  the  retinae  receive  their  light  from  the  left  side  of  the 
median  plane  of  the  body;  the  unshaded  portions,  from  the  right 
side.  The  nasal  part  of  each  retina  recives  visual  images  from 
objects  lying  on  the  same  side  of  the  body  exclusively,  i.  e., 
from  the  temporal  portion  of  the  visual  field,  while  the  temporal 
part  of  the  retina  may  receive  images  from  objects  on  the  oppo- 
site side  of  the  body.  Accordingly,  in  order  that  the  visual 
images  derived  from  all  objects  lying  on  one  side  of  the  body  may 
be  represented  by  nervous  excitations  within  the  opposite  half 
of  the  brain,  it  is  necessary  that  the  nerve-fibers  from  the  nasal 
part  of  each  retina  cross  in  the  chiasma,  while  those  from  the 
temporal  part  pass  through  the  chiasma  without  decussation. 

The  reflex  optic  centers  in  the  roof  of  the  midbrain  occupy 
most  of  the  colliculus  superior,  which  corresponds  to  the  optic 

14 


210 


INTRODUCTION   TO   NEUROLOGY 


"""'i^lLo^e 


Kigi^^ 


Fig.  101. 


THE    VISUAL    APPARATUS  211 

lobe  of  the  fish  brain  (Figs.  43,  44).  Here  visual  impressions 
are  brought  into  physiological  relations  with  those  of  the  tactual 
and  auditory  systems  received  by  the  lemnisci.  The  chief  effer- 
ent pathway  from  this  center  is  by  way  of  the  underlying  cere- 
bral peduncle  (Fig.  75).  Here  reflex  connections  are  effected 
directly  with  the  nuclei  of  the  III  and  IV  cranial  nerves  for  the 
eye  muscles,  and  through  the  fasciculus  longitudinalis  medialis 
with  the  centers  for  all  other  cranial  and  spinal  muscles.  This 
fasciculus  is  a  strong  bundle  composed  of  both  descending  and 
ascending  fibers  whose  function  is  the  general  coordination  of 
reflex  motor  responses,  and  in  particular  those  of  the  conjugate 
movements  of  the  two  eyes  (see  p.  186). 

The  accommodation  of  the  eye  for  distance  is  effected  by 
changes  in  the  curvature  of  the  lens,  and  the  adaptation  for 
differences  in  illumination  is  effected  in  part  by  changes  in  the 
diameter  of  the  pupil  (this  is  in  addition  to  the  changes  in  the 
retinal  pigment  referred  to  on  p.  207  and  to  changes  in  the  rods 
and  cones  and  other  neurons  of  the  retina  which  may  be  excited 
by  the  centrifugal  fibers  from  the  brain  to  the  retina  referred  to 
on  p.  209).  The  nerves  controlling  the  movements  of  the  lens 
and  the  pupillary  reactions  belong  to  the  visceral  motor  system. 
They  leave  the  central  nervous  system  in  part  through  the  ocu- 
lomotor nerve  and  in  part  (for  dilation  of  the  iris)  from  the  lower 
cervical  region  of  the  spinal  cord.  The  latter  fibers  pass  by  way 
of  roots  of  spinal  nerves  into  the  superior  cervical  sympathetic 
ganghon  (p.  234  and  Fig.  41,  p.  107)  and  then  forward  to  the 
eyeball.  We  cannot  here  enter  into  further  details  of  the  mech- 
anism of  accommodation  or  of  the  diopteric  apparatus  and  the 
accessory  parts  of  the  eye;  see  the  larger  text-books  of  anatomy 
and  physiology. 

The  thalamic  connections  of  the  optic  tracts  in  the  lowest 
vertebrates  are  very  insignificant,   collaterals  of  these  fibers 


Fig.  101. — A  diagram  of  the  visual  tract,  illustrating  the  significance  of 
the  partial  decussation  of  nerve-fibers  in  the  optic  chiasma  so  as  to  ensure 
the  representation  in  the  cerebral  cortex  of  nervous  impulses  excited  by  ob- 
jects on  the  opposite  half  of  the  body  only.  ///,  Oculomotor  nerve;  L, 
medial  lemniscus;  M,  mammillary  bodies;  7? A'',  red  nucleus  (nucleus  ruber); 
SN,  black  substance  (substantia  nigra) ;  TG,  optic  tract  to  corpora  quadri- 
gemina  (cf.  Fig.  75).     (From  Starr's  Nervous  Diseases.) 


212  INTRODUCTION  TO  NEUROLOGY 

being  given  off  to  terminate  in  the  unspecialized  correlation 
centers  of  the  dorsal  part  of  the  thalamus.  But  in  all  forms  with 
a  differentiated  cerebral  cortex  these  thalamic  optic  connections 
assume  greater  importance,  a  special  region  in  the  dorsal  part 
of  the  thalamus  being  set  apart  for  their  use.  Thus  arose  the 
lateral  geniculate  body,  and  in  higher  mammals  this  is  supple- 
mented by  the  pulvinar.  These  centers  are,  in  the  strict  sense 
of  the  word,  cortical  dependencies,  for  they  attain  to  only  very 


Fig.  102. — Section  through  the  parietal  eye  of  a  lizard  (Anguis  fragilis) : 
ct,  Connective-tissue  cells  around  nerve;  gc,  ganglion  cells;  I,  lens;  n,  nerve- 
fibers;  pc,  pigment  cells;  pre,  parietal  nerve  from  the  parietal  eye  to  the 
brain;  r,  retinal  cells;  vh,  vitreous  body.     (After  Nowikoff.) 

insignificant  proportions  in  forms  with  rudimentary  cerebral 
cortex,  but  increase  in  proportion  to  the  elaboration  of  the  visual 
cortex. 

The  early  steps  in  the  evolution  of  the  eyes  of  vertebrates  are  imperfectly 
understood.  In  structure  and  mode  of  function  the  vertebrate  eyes  are 
unlike  those  of  any  of  the  invertebrate  animals.  The  experiments  of  Parker 
and  others  have  shown  that  the  skin  of  many  aquatic  vertebrates  among  the 
fishes  and  amphibians  is  sensitive  to  light,  and  it  has  been  supposed  that  the 
vertebrate  retina  was  differentiated  from  such  cutaneous  photoreceptors. 
But  it  seems  more  probable  (Parker,  1908)  that  the  vertebrate  organs  of 
vision  were  developed  from  the  first  within  the  central  nervous  system. 

Some  of  the  fishes  and  reptiles  possess,  in  addition  to  lateral  eyes  of 
typical  form,  a  median  eye,  the  parietal  or  pineal  eye  (Fig.  102),  which  is 


THE    VISUAL    APPARATUS  213 

developed  from  a  tubular  outgrowth  from  the  roof  of  the  diencephalon  (the 
pineal  organ  or  epiphysis,  p.  162);  this  extends  dorsalward  from  the  brain 
through  a  special  foramen  in  the  skull  to  reach  the  skin  in  the  center  of 
the  top  of  the  head.  The  functions  and  evolutionary  significance  of  this 
eye  are  shrouded  in  mystery. 

Summary. —  The  retina  is  developed  as  a  lateral  outgrowth 
from  the  early  neural  tube  and  throughout  life  retains  its  char- 
acter as  a  part  of  the  brain,  the  "optic  nerve"  being  really  a  cor- 
relation tract  comparable  with  the  lemniscus  systems.  The  rods 
and  cones  of  the  retina  are  the  photoreceptors  and  also  the  neu- 
rons of  the  first  order  in  the  optic  path.  The  "optic  nerve"  con- 
tains neurons  of  the  third  order  from  the  retina  to  the  thalamus 
and  midbrain,  and  also  centrifugal  fibers  from  the  midbrain  to 
the  retina.  In  lower  vertebrates  the  fibers  of  the  optic  path 
decussate  completely  in  the  optic  chiasma,  but  in  those  mammals 
whose  fields  of  vision  overlap  there  is  an  incomplete  decussation 
so  as  to  ensure  the  representation  of  the  field  of  vision  of  one  side 
completely  in  the  opposite  cerebral  hemisphere.  Those  fibers 
of  the  optic  tract  which  terminate  in  the  midbrain  effect  various 
kinds  of  reflex  connections,  while  those  which  terminate  in  the 
thalamus  effect  cortical  connections.  The  parietal  or  pineal 
eye  of  some  fishes  and  reptiles  is  apparently  functional  as  an 
organ  of  vision  which  was  developed  quite  independently  of 
the  lateral  eyes. 

Literature 

In  this  chapter  we  have  not  attempted  to  present  a  systematic  descrip- 
tion of  the  structure  of  the  eye  or  of  the  functions  of  the  retina  and  theories 
of  vision.  For  the  details  of  these  questions  reference  must  be  made  to  the 
larger  text-books  of  anatomy,  physiology,  and  phj'siological  psj'chologj'. 
A  few  general  works  are  cited  below,  together  with  some  special  researches 
to  which  reference  has  been  made  in  the  preceding  text: 

VON  Bechterew,  W.  1909.  Die  Funktionen  der  Nervencentra,  Jena, 
Bd.  2,  pp.  996-1103.     Idem,  1911,  Bd.  3,  pp.  1554-1583,  IS837I964. 

Cole,  L.  J.  1907.  An  Experunental  Study  of  the  Image-forming  Powers 
of  Various  Types  of  Eyes,  Proc.  Amer.  Acad.  Arts  and  Sciences,  vol.  xhi, 
No.  16. 

Harris,  W.  1904.  Binocular  and  Stereoscopic  Vision  in  Man  and  Other 
Vertebrates,  with  Its  Relation  to  the  Decussation  of  the  Optic  Xerves,  the 
Ocular  Movements,  and  the  Pupil  Light  Reflex,  Brain,  vol.  xxvii,  pp.  106- 
147. 

Ladd,  G.  T.,  and  Woodworth,  R.  S.  1911.  Elements  of  Physiological 
Psychology,  New  York. 

Mast,  S.  O.  1911.  Light  and  the  Behavior  of  Organisms,  New  York. 


214  INTRODUCTION  TO  NEUROLOGY 

NuEL,  J.  P.  1904.  La  Vision,  Bibliotheque  Internationale  de  Psychologic 
Experimentale  Normal  et  Pathologique,  Paris. 

Parker,  G.  H.  1908.  The  Origin  of  the  Lateral  Eyes  of  Vertebrates, 
Amer.  Nat.,  vol.  xhi,  pp.  601-609. 

— .  1909.  The  Integumentary  Nerves  of  Fishes  as  Photoreceptors  and 
Their  Significance  for  the  Origin  of  the  Vertebrate  Eyes,  Amer.  Jour,  of 
Physiol.,  vol.  xxv,  pp.  77-80. 

Ramon  y  Cajal,  S.  1894.  Die  Retina  der  Wirbeltiere,  Wiesbaden. 

ScHAFER,  E.  A.  Text-book  of  Physiology,  vol.  h,  pp.  752-761,  1026- 
1148. 

Vincent,  S.  B.  1912.  The  Mammalian  Eye,  Jour.  Animal  Behavior, 
vol.  ii,  pp.  249-255. 

Watson,  J.  B.  1914.  Behavior,  an  Introduction  to  Comparative  Psy- 
chology, New  York,  Chapter  XL 


CHAPTER  XV 

THE    OLFACTORY   APPARATUS 

The  olfactory  part  of  the  brain  as  a  whole  is  sometimes  called 
the  rhinencephalon.  In  fishes  (p.  112  and  Figs.  43,  44)  almost  the 
whole  of  the  cerebral  hemisphere  is  devoted  to  this  function,  and 
as  we  pass  up  the  scale  of  animal  life  more  and  more  non-ol- 
factory centers  are  added  to  the  hemisphere  in  the  corpus  stria- 
tum and  cerebral  cortex,  until  in  man  the  non-olfactory  part  of 
the  hemisphere  overshadows  the  rhinencephalon.  The  complex 
form  of  the  human  cerebral  hemisphere  cannot  be  adequately 
understood  apart  from  a  knowledge  of  this  evolutionary  history, 
which  has  been  studied  with  great  care  by  comparative  neurolo- 
gists. The  metamorphosis  of  the  vertebrate  cerebral  hemisphere 
from  a  simple  olfactory  reflex  apparatus  in  the  lower  fishes  to  the 
great  organ  of  the  higher  mental  processes  upon  which  all  human 
culture  depends  is  a  very  dramatic  history,  into  which,  unfortu- 
nately, we  cannot  here  enter. 

Smell  is  evidently  the  dominant  sense  in  many  of  the  lower 
vertebrates.  That  this  is  the  case  in  the  dogfish  is  shown  by  the 
enormous  development  of  the  olfactory  centers  of  the  brain,  to 
which  reference  has  just  been  made.  And  in  most  of  the  labora- 
tory mammals,  such  as  the  rat  and  the  dog,  the  sense  of  smell 
still  plays  a  very  much  more  important  part  in  the  behavior 
complex  than  in  man  and  other  primates,  whose  olfactory  organs 
are  in  a  reduced  condition. 

The  ncri'us  terminalis  is  a  slender  ganglionated  nerve  found  associated 
with  the  olfactory  nerve  in  most  classes  of  vertebrates  from  fishes  to  man. 
Its  fibers,  which  are  unmyelinated,  reach  the  mucous  membrane  of  the 
nose,  though  the  precise  method  of  their  ending  is  unknown.  They  pass 
inward  in  company  with  those  of  the  oKactory  nerve  as  far  as  the  olfactory 
bulb.  Here  they  separate  from  the  olfactory  fibers  and  enter  the  cerebral 
hemisphere  between  the  attachment  of  the  olfactory  bulb  and  the  lamina 
terminaKs  (Fig.  43,  p.  111).  Within  the  brain  they  have  been  followed 
backward  through  the  entire  length  of  the  olfactory  area  and  hypothalainus, 
but  their  cerebral  connections  have  never  been  acciu^ately  determined. 
The  function  of  this  nerve  is  likewise  wholly  unknown. 

215 


216 


INTRODUCTION   TO    NEUROLOGY 


The  olfactory  cerebral  centers  fall  into  two  groups:  (1)  the 
reflex  centers  of  the  brain  stem  and  (2)  the  olfactory  cerebral 
cortex.  The  arrangements  of  the  olfactory  reflex  centers  and 
their  connecting  tracts  are  essentially  similar  in  plan  in  all  ver- 
tebrate brains  (except  in  some  aquatic  mammals,  like  the  dol- 
phin, which  lack  olfactory  organs  altogether).  The  olfactory 
cerebral  cortex,  on  the  other  hand,  is  very  diversely  developed 
in  different  groups  of  vertebrates.  There  is  no  true  cerebral 
cortex  in  fishes;  in  amphibians  (particularly  in  the  frog)  the 
olfactory  cerebral  cortex  begins  to  emerge  from  the  general 


Fig.  103. — Dissection  of  the  right  olfactory  bulb  and  nerve  on  the 
lateral  wall  of  the  nasal  cavity.  (From  Wood's  Reference  Handbook  of  the 
Medical  Sciences.) 

olfactory  reflex  centers;  in  reptiles  there  is  a  well-formed  olfac- 
tory cortex  of  simple  histologic  pattern  and  the  beginnings  of  the 
non-olfactory  cortex;  in  birds  the  olfactory  apparatus  is  reduced 
and  the  non-olfactory  cortex  is  somewhat  more  extensive  than 
in  reptiles;  in  mammals  both  the  olfactory  cerebral  cortex  and 
the  non-olfactory  cortex  attain  their  maximum  dimensions,  the 
former  in  the  lowest  members  of  this  group  and  the  latter  in  the 
highest. 

The  cerebral  cortex  as  a  whole  is  sometimes  called  the 
pallium.  That  portion  of  the  paUium  which  is  related  with  the 
olfactory  apparatus  was  differentiated  earlier  in  vertebrate  evo- 


THE  OLFACTORY  APPAEATUS 


217 


lution  than  the  non-olfactory  pallium  and  has,  therefore,  been 
called  the  archipallium.  The  non-olfactory  cerebral  cortex  is 
termed  the  neopallium  (or  somatic  pallium,  for  it  receives  the 
somatic  projection  fibers).  The  archipallium,  as  already  indi- 
cated, attains  its  maximum  development  in  the  lowest  mammals, 
particularly  the  marsupials,  like  the  kangaroo  and  opossum, 
consisting  of  the  hippocampus  and  hippocampal  gyrus  (gyrus 
hippocampi,  or  pyriform  lobe).  The  neopallium  attains  its 
maximum  size  in  the  human  brain,  and  the  indications  are  that 
in  civilized  races  it  is  now  in  process  of  further  differentiation. 
In  the  human  brain  practically  all  parts  of  the  exposed  cerebral 
cortex  are  neopaUium,  the  archipallium  being  of  relatively  small 


Olfactory  tract 


Granule  cell 
Mitral  cell 
Glomerulus 
Olfactory  nerve 
Ethmoid  bone 
Olfactory  epithelium 


Fig.  104. — Diagram  of  the  connections  of  the  olfactory  bulb. 


size  and  mostly  concealed  by  a  process  of  infolding  along  the 
posterior  margin  of  the  neopallium. 

In  the  human  body  the  specific  olfactory  receptors  (see  p.  92) 
are  Hmited  to  a  small  area  of  the  mucous  lining  in  the  upper  part 
of  the  nasal  cavity  on  both  its  lateral  (Fig.  103)  and  its  medial 
walls.  The  cell  bodies  of  the  olfactory  neurons  of  the  first 
order  lie  in  this  mucous  membrane  (Figs.  36  and  104).  The 
axons  of  these  neurons  form  the  fibers  of  the  olfactory''  nerve, 
which  are  unmyelinated;  they  pierce  the  ethmoid  bone  in  nu- 
merous small  fascicles  (fila  olfactoria)  and  terminate  by  free 
arborizations  in  the  primary  olfactory  center  within  the  olfac- 
tory bulb  (Figs.  53,  78,  103,  104).  Several  olfactory  nerve- 
fibers   terminate  together   in  a  dense  entanglement  of  fibers 


218  INTRODUCTION   TO    NEUROLOGY 

termed  a  glomerulus,  which  also  receives  one  or  more  dendrites 
from  the  olfactory  neurons  of  the  second  order,  or  mitral  cells. 
The  glomerulus,  therefore,  contains  the  first  synapse  in  the  ol- 
factory pathway.  The  axons  of  the  mitral  cells  form  the  ol- 
factory tract  and  discharge  into  the  olfactory  area,  or  secondary 
olfactory  nucleus,  at  the  base  of  the  olfactory  bulb.  These  axons 
give  off  collateral  branches  which  discharge  among  very  small 
neurons  of  the  olfactory  bulb,  the  granule  cells,  whose  chief 
processes  are  directed  peripheralward,  to  end  among  dendrites 
of  the  mitral  cells. 

Attention  has  already  been  called  (pp.  75  and  91)  to  the  fact 
that,  though  smell  and  taste  are  both  chemically  excited  senses, 
the  olfactory  organs  can  be  excited  by  much  more  dilute  solu- 
tions of  the  stimulating  substances  than  can  the  gustatory  or- 
gans. The  lowering  of  the  threshold  for  olfactory  stimuli  has 
been  effected  by  several  means,  among  which  we  may  mention 
the  following:  Whereas  in  the  taste-buds  there  is  a  synapse 
between  the  specific  receptor  cells  and  the  peripheral  nerve-fiber 
(Fig.  35,  p.  91),  there  is  no  such  synapse  in  the  olfactory  organ, 
the  peripheral  receptor  cell  giving  rise  directly  to  the  olfactory 
nerve-fiber  (Fig.  104).  In  the  second  place,  the  peripheral 
gustatory  nerve-fiber  discharges  centrally  into  several  neurons 
of  the  primary  gustatory  center  in  the  medulla  oblongata;  but 
many  peripheral  olfactory  fibers  enter  a  single  glomerulus,  where 
they  are  engaged  by  dendrites  from  only  one  or  two  mitral  cells, 
thus  providing  for  the  summation  of  stimuh  in  each  mitral  cell. 
Again,  the  collateral  discharge  from  the  olfactory  tract  into  the 
granule  cells  (which  are  very  numerous)  carries  the  discharge 
from  the  mitral  cells  back  again  into  these  cells  and  thus  rein- 
forces their  discharge  (see  pp.  101,  192).  By  these  and  other 
devices  exceedingly  feeble  peripheral  stimuH  may  give  rise  to 
very  strong  excitations  in  the  olfactory  centers. 

The  fibers  of  the  olfactory  tract  reach  the  olfactory  area,  or 
secondary  center,  by  three  paths  which  spread  out  from  the 
base  of  the  olfactory  bulb  and  are  known  as  the  medial,  inter- 
mediate, and  lateral  olfactory  strise  (these  are  shown  but  not 
named  on  Fig.  53,  p.  120).  The  olfactory  area  has  various  sub- 
divisions (Fig.  105),  the  most  important  of  which  are:  (1)  the 
lateral  olfactory  nucleus  (or  gyrus)  which  receives  the  lateral 


THE  OLFACTORY  APPARATUS 


219 


olfactory  stria  and  extends  backward  directly  into  the  tip  of  the 
temporal  lobe  of  the  cerebral  cortex  (uncus),  where  the  ventro- 
lateral ends  of  the  hippocampus  and  the  hippocampal  gyrus  come 
together;  (2)  the  medial  olfactory  nucleus,  including  the  sub- 
callosal gyrus  (Fig.  52,  p.  119)  and  septum,  which  receive  the 
medial  olfactory  stria;  (3)  the  intermediate  olfactory  nucleus, 
which  occupies  the  anterior  perforated  substance  (Figs.  53,  105) 
and  receives  the  intermediate  olfactory  stria.  These  nuclei  are 
all  important  reflex  centers,  where  olfactory  stimuli  are  combined 


Olfactory  bulb 


Lateral  olfactory  gyruS' 
(stria) 

Posterior  parolfactory, 
sulcus 

Uncus  (hippocampal 
gyrus) 


^%    ^Medial  olfactory  gyrus  (stria) 


Olfactory  tract 


Limen  insulas 

Anterior  perforated 
substance 


Hippocampal  gyrus 


Fig.  105. — Brain  of  a  human  fetus  at  the  beginning  of  the  fifth  month 
(22.5  cm.  long),  illustrating  the  olfactory  centers  visible  on  the  ventral 
surface.     (After  Retzius,  from  Morris'  Anatomy.) 


with  other  sensory  impressions,  each  nucleus  having  its  own  par- 
ticular reflex  pattern.  The  intermediate  nucleus  (also  called 
tuberculum  olfactorium  and  by  Edinger  lobus  parolfactorius)  is 
better  developed  in  many  other  mammals  than  in  man,  and  is 
probably  especially  concerned  with  the  feeding  reflexes  of  the 
snout  or  muzzle,  including  smell,  touch,  taste,  and  muscular 
sensibility,  a  physiological  complex  which  Edinger  has  called 
collectively  the  "oral  sense."  This  complex  of  muzzle  reflexes 
has  probably  played  a  very  important  role  in  the  earlier  stages 
of  the  evolutionary  history  of  the  correlation  centers  of  the 


220 


INTRODUCTION   TO    NEUROLOGY 


cerebral  hemispheres  (see  the  works  by  Edinger  cited  at  the  end 
of  this  chapter). 

From  these  nuclei  of  the  olfactory  area  fiber  tracts  of  the  third 
order  pass  to  the  mammillary  bodies  of  the  hypothalamus  and 
to  the  habenular  bodies  of  the  epithalamus,  from  both  of  which, 
after  another  synapse,  tracts  lead  downward  into  the  motor 


form.  bulb. 


Th:olT.hLjpth> 


^com.Qnt 
^n.  pop. 


Fig.  106. — Diagram  of  some  of  the  olfactory  tracts  in  the  brain  of  the 
rat.  The  chief  connections  of  the  medial-  and  intermediate  olfactory  tracts 
are  indicated;  those  of  the  lateral  olfactory  tract  are  omitted:  c.mam., 
corpus  mamillare;  col.  forn.,  columna  fornicis;  com.  ant.,  commissura  an- 
terior; com.  hip.,  commissura  hippocampi;  com.  post.,  commissura  posterior; 
form,  bulb.,  formatio  bulbaris;  f.retr.,  fasciculus  retroflexus  of  Meynert; 
hab.,  habenula;  h.pc,  hippocampus  precommissuralis;  h.sc,  hippocampus 
supracommissuralis ;  n.  ant.,  nucleus  anterior  thalami;  n.  olf.  ant.,  nucleus 
olfactorius  anterior;  n.  pop.,  nucleus  preopticus  (ganglion  opticum  basale); 
S,  septum;  str.  med.,  stria  meduUaris  thalami;  tr.  mam.  th.,  tractus  mamillo- 
thalamicus  (Vicq  d'Azyri) ;  tr.  olf.  hypth.,  tractus  olfacto-hypothalamicus,  or 
basal  olfactory  tract;  tr.  olf.  tegm.,  tractus  olfacto-tegmentalis;  tub.  f.  dent., 
tuberculum  fasciae  dentatse  (hippocampus  postcommissuralis) ;  tub.  olf., 
tuber culum  olfactorium. 


centers  of  the  midbrain  in  the  cerebral  peduncle.  The  path  from 
the  mammillary  body  is  the  tractus  mamillo-peduncularis  (Figs. 
75,  78,  106).  The  path  from  the  habenular  body  is  the  tractus 
habenulo-peduncularis  (fasciculus  retroflexus  B.  N.  A.,  or  Mey- 
nert's  bundle — Fig.  106).  The  mammillary  body  also  sends  a 
tract  into  the  anterior  nucleus  of  the  thalamus,  the  tractus  mam- 
illo-thalamicus  (fasciculus  thalamo-mamillaris  B.  N.  A.,  or  tract 


THE  OLFACTORY  APPARATUS  221 

of  Vicq  d'Azyr,  Figs.  78, 106),  for  the  correlation  of  olfactory  with 
general  somatic  reactions.  There  is  also  a  direct  path  between 
the  secondary  olfactory  area  and  the  cerebral  peduncle,  without 
connection  with  the  diencephalon,  by  way  of  the  tractus  olfacto- 
tegmentalis  (Fig.  106).  In  the  epithalamus  the  olfactory  ner- 
vous impulses  are  correlated  with  those  of  the  somatic  sensory 
centers  of  the  thalamus,  especially  the  optic  and  tactual  sys- 
tems (p.  162) ;  in  the  hypothalamus  they  are  correlated  with  gus- 
tatory and  various  visceral  sensory  systems  (p.  163). 

The  preceding  account  includes  a  description  of  a  few  of  the 
more  important  pathways  involved  in  olfactory  reflexes.  Ol- 
factory impulses  which  reach  the  cerebral  cortex  take  a  different 
path.  They  are  carried  from  all  parts  of  the  secondary  olfactory 
area  at  the  base  of  the  olfactory  bulb  into  the  hippocampus 
(which  composes  the  greater  part  of  the  archipallium  in  the 
human  brain)  by  several  olfacto-cortical  tracts,  whose  courses 
in  the  human  brain  are  so  tortuous  that  we  shall  not  attempt  to 
describe  them  here. 

The  hippocampus  (formerly  called  the  Ammon's  horn  or  cornu 
Ammonis,  also  the  hippocampus  major.  Fig.  107)  is  a  special 
convolution  which  forms  the  postero-ventral  border  of  the  cere- 
bral cortex;  it  is  rolled  into  the  posterior  horn  of  the  lateral 
ventricle  so  that  it  does  not  appear  on  the  surface  of  the  brain. 
It  is  connected  with  the  remainder  of  the  cortex  (neopallium) 
by  cortex  of  transitional  type,  the  hippocampal  gyrus  (gyrus 
hippocampi),  from  which  it  is  separated  by  a  deep  groove,  the 
fissura  hippocampi.  The  free  border  of  the  hippocampus  is 
accompanied  for  its  entire  length  by  a  strong  band  of  fibers,  the 
fimbria,  through  which  olfactory  projection  fibers  enter  it  from 
the  secondary  olfactory  area.  These  fibers  discharge  into  a 
subsidiary  part  of  the  hippocampus,  the  dentate  gyrus  (gyrus 
dentatus,  also  called  fascia  dentata),  at  a,  Fig.  107. 

The  hippocampus  is  connected  with  all  other  parts  of  the  cere- 
bral cortex  by  an  extensive  system  of  association  tracts  forming 
the  alveus  (Fig.  107),  thus  providing  for  those  complex  inter- 
actions of  diverse  functional  systems  for  which  the  cortex  is 
especially  adapted.  There  is  also  an  efferent  pathway  from  the 
hippocampus  to  the  brain  stem  through  the  fimbria  and  the 
column  of  the  fornix  (Figs.  78,  107),  whose  fibers  terminate  in 


222 


INTRODUCTION   TO    NEUROLOGY 


both  the  hypothalamus  and  the  epithalamus.  This  is  the  prob- 
able pathway  taken  by  voluntary  motor  impulses  of  cortical 
origin,  in  which  the  olfactory  element  is  dominant,  such  as 
sniffing.  Having  reached  the  hypothalamus  and  epithalamus, 
these  motor  impulses  of  cortical  origin  are  conveyed  to  the  motor 
centers  in  the  midbrain  by  the  same  pathways  as  are  the  reflex 
impulses  already  described. 


Fig.  107. — Section  across  the  hippocampus  and  gyrus  hippocampi  of  the 
human  brain.     (After  Edinger.) 

Summary. — The  olfactory  centers  (rhinencephalon)  make  up 
nearly  the  entire  forebrain  in  fishes,  and  in  higher  vertebrates 
progressively  more  non-olfactory  centers  are  added  to  this  part 
of  the  brain.  The  non-olfactory  parts  of  the  cerebral  hemi- 
sphere comprise  chiefly  the  corpus  striatum  and  the  neopalhum; 


THE  OLFACTORY  APPARATUS  223 

the  latter  makes  up  by  far  the  larger  part  of  the  human  hemi- 
sphere. The  rhinencephalon  consists  of  a  reflex  part  in  the  brain 
stem  and  a  cortical  part  in  the  archipallium.  Smell  and  taste  are 
both  chemically  excited  senses,  but  the  threshold  of  excitation  is 
much  lower  in  the  case  of  smell.  This  is  brought  about  by  the 
suppression  of  a  synapse  in  the  peripheral  receptor  organ  and  by 
a  complex  mechanism  for  the  summation  and  reinforcement  of 
stimuli  in  the  primary  olfactory  center  in  the  olfactory  bulb. 
The  secondary  olfactory  center  is  the  olfactory  area,  which  has 
three  parts,  each  of  which  is  a  reflex  center  of  distinctive  type. 
The  reflex  path  from  the  secondary  center  passes  backward  to 
the  epithalamus  and  to  the  hypothalamus,  from  both  of  which  a 
descending  path  goes  to  the  motor  centers  in  the  cerebral 
peduncle.  The  secondary  olfactory  center  also  discharges  into 
the  olfactory  cerebral  cortex,  which  is  chiefly  contained  within 
the  hippocampus  and  from  which  manifold  association  pathways 
connect  with  all  other  parts  of  the  cerebral  cortex. 

Literature 

Barker,  L.  F.  1901.  The  Nervous  System,  New  York,  pp.  747-781. 

Edinger,  L.  1908.  Vorlesungen  iiber  den  Bau  der  nervosen  Zentral- 
organe,  Bd.  2,  Vergleichende  Anatomie  des  Gehirns,  Leipzig. 

— .  1908.  The  Relations  of  Comparative  Anatomy  to  Comparative 
Psychology,  Jom-.  Comp.  Neurology,  vol.  xviii,  pp.  437-457. 

— .  1908.  Ueber  die  Oralsinne  dienenden  Apparate  am  Gehirn  der 
Sanger,  Deutsch.  Zeits.  f.  Nervenheilkunde,  Bd.  36. 

Herrick,  C.  Judson.  1908.  On  the  Phylogenetic  Differentiation  of 
the  Organs  of  Smell  and  Taste,  Jour.  Comp.  Neurology,  vol.  xviii,  pp. 
157-166. 

— .  1910.  The  Evolution  of  Intelligence  and  Its  Organs,  Science,  N.  S., 
vol.  xxxi,  pp.  7-18. 

— .  1910.  The  Morphology  of  the  Forebrain  in  Amphibia  and  Reptilia, 
Jour.  Comp.  Neurology,  vol.  xx,  pp.  413-547. 

Johnston,  J.  B.  1906.  The  Nervous  Svstem  of  Vertebrates,  Phila- 
delphia, pp.  176-189,  292-337. 

— .  1909.  The  Morphology  of  the  Forebrain  Vesicle  in  Vertebrates, 
Jour.  Comp.  Neurology,  vol.  xix,  pp.  457-539. 

— .  1913.  The  Morphology  of  the  Septimi,  Hippocampus  and  Pallial 
Commissure  in  Reptiles  and  Mammals,  Jour.  Comp.  Neurology,  vol.  xxiii, 
pp. 371-478. 

Kappers,  C.  U.  a.  1908.  Die  Phylogenese  des  Rhinencephalons,  des 
Corpus  Striatum  vmd  der  Vorderhirnkommissuren,  Folia  Ncurobiologica, 
Bd.  1,  pp.  173-288. 

Zwaardemaker,  H.  1895.  Die  Physiologie  des  Gcruchs,  Leipzig. 

— .  1900.  Revue  gencrale  sur  I'olfaction,  Annee  Psychol.,  vol.  vi. 

— .  1902.  Geruch.  Ergebnisse  der  Physiologie,  Bd.  1. 


CHAPTER  XVI 

THE    SYMPATHETIC    NERVOUS    SYSTEM 

Before  we  can  extend  our  analysis  of  the  conduction  paths 
into  the  realm  of  the  visceral  activities  of  the  body  we  must  con- 
sider briefly  the  sympathetic  nervous  system  through  which  the 
regulatory  control  of  these  activities  is  effected.  Most  of  the 
visceral  activities  are  performed  either  unconsciously  or  with 
very  imperfect  awareness.  The  nervous  mechanisms  of  many 
of  them  are  still  obscure.  Nevertheless  the  visceral  functions 
as  a  whole  are  of  enormous  importance,  not  only  in  the  mainte- 
nance of  the  physical  welfare  of  the  body,  but  also  as  the  organic 
background  of  the  entire  conscious  life  (see  p.  259). 

Many  of  the  visceral  functions  can  be  performed  quite  apart 
from  any  nervous  control  whatever  by  the  intrinsic  mechanisms 
of  the  viscera  themselves.  The  heart  musculature,  for  instance, 
beats  automatically  with  a  characteristic  rhythm,  and  most  of 
the  other  visceral  muscles  have  the  power  of  automatic  rhythmic 
contraction.  Some  of  the  glands  of  the  body  may  be  excited 
to  secretion  by  chemical  substances  dissolved  in  the  blood.  For 
instance,  when  food  enters  the  small  intestine  from  the  stomach, 
the  intestinal  glands  are  directly  excited  to  activity  by  the  pres- 
ence of  the  food.  Some  of  their  secretions  are  poured  out  into 
the  intestine  to  act  as  digestive  juices;  others  are  absorbed  di- 
rectly by  the  blood  (internal  secretions) .  Among  the  latter  is 
secretin,  a  substance  which  is  carried  by  the  blood-stream  to  the 
pancreas  and  there  excites  the  secretory  activity  of  this  organ  to 
the  formation  of  pancreatic  juice,  which  is,  in  turn,  poured  into 
the  intestine.  The  very  complex  secretory  activities  involved  in 
the  formation  of  the  intestinal  and  pancreatic  juices  under  the 
stimulus  offered  by  the  presence  of  food  in  the  intestine,  there- 
fore, are  not  directly  excited  by  the  nervous  system,  though  they 
may  be  brought  under  nervous  control  in  a  secondary  way. 

Most  of  the  viscera  are,  however,  under  immediate  nervous 
control  of  two  sorts.     This  control  is  partly  derived  from  the 

224 


THE    SYMPATHETIC    NERVOUS    SYSTEM  225 

ganglia  of  the  sympathetic  nervous  system  which  are  distributed 
widely  throughout  the  body,  and  partly  from  the  central  nervous 
system.  The  nervous  impulses  involved  in  the  second  type  of 
control  are,  moreover,  always  distributed  to  the  viscera  through 
the  sympathetic  system. 

A  clear  analytic  description  of  the  visceral  nervous  systems  is 
extremely  difficult,  and  there  is  wide  diversity  of  usage,  not  only 
in  the  terminology  employed  in  these  descriptions,  but  also  in 
the  fundamental  concepts  upon  which  they  are  based.  The 
brain  and  spinal  cord  and  the  cranial  and  spinal  nerves  and  their 
end-organs  in  the  aggregate  constitute  the  cerebrospinal  nervous 
system.  The  cell  bodies  of  the  neurons  of  this  system  all  lie 
within  the  spinal  cord  and  brain  (including  the  retina)  or  in  the 
ganglia  on  the  sensory  roots  of  the  cranial  and  spinal  nerves. 
There  are,  however,  innumerable  other  ganglia  distributed  very 
widely  throughout  the  body,  which  are  connected  with  each 
other  and  with  the  central  nervous  system  by  intricate  nervous 
plexuses.  These  constitute  the  sympathetic  ganglia  and  nerves, 
or  in  the  aggregate  the  sympathetic  nervous  system. 

There  is  an  especially  important  group  of  sympathetic  ganglia 
which  are  arranged  in  two  longitudinal  series  extending  one  on 
each  side  of  the  vertebral  column.  These  ganglia  constitute  the 
vertebral  sympathetic  trunks  or  chains,  and  throughout  the 
middle  part  of  the  body  there  is  one  ganglion  of  each  trunk  for 
each  spinal  root  (Fig.  41,  p.  107).  Communicating  branches  con- 
nect the  gangha  of  the  trunks  with  their  respective  spinal  roots, 
and  from  these  ganglia  sympathetic  nerves  extend  out  periph- 
erally to  ramify  among  the  viscera  and  other  tissues  of  the 
body.  Ganglion  cells  are  scattered  among  these  peripheral 
sympathetic  nerves,  and  in  some  places,  especially  among  the 
abdominal  viscera,  these  cells  are  crowded  together  to  form  large 
ganglionic  plexuses  (Fig.  108). 

When  further  analyzed,  the  sympathetic  nervous  system  is 
found  to  consist  of  two  imperfectly  separable  parts.  The  first 
is  a  diffusely  arranged  peripheral  plexus  of  nerve-cells  and  fibers 
adapted  for  the  local  control  of  the  organs  with  which  it  is  con- 
nected. This  we  shall  call  the  peripheral  autonomous  part  of  the 
sympathetic  system  (this  is  not  the  same  as  the  autonomic  ner- 
vous system  of  Langley,  see  p.  229).     The  second  part  of  the 

15 


226 


INTRODUCTION   TO    NEUROLOGY 


Maxillary  nerve 

Ciliary  ganglion 
Sphenopalatine  ganglion 
Superior  cervical  ganglion  of  sympathetic 


Cervical  plexus 


Brachial  plexus 


Greater  splanchnic  nerve 


Lesser  splanchnic  nerve 


Lumbar  plexus 


Sacral  plexus 


Pharyngeal  plexus 

Middle  cervical  ganglion  of 

sympathetic 
Inferior  cervical  g.  of  sympathetic 
-Recurrent  nerve 

Bronchial  plexus 


Cardiac  plexus 


Esophageal  plexus 
::=Coronary  plexus 


Left  vagus  nerve 

Gastric  plexus 
■Celiac  plexus 

■Superior  mesenteric  plexus 

Aortic  plexus 

Inferior  mesenteric  plexus 

Hypogastric  plexus 

■Pelvic  plexus 

■Bladder 
Vesical  plexus 


Fig.  108. — The  sympathetic  nervous  system,  illustrating  the  right  sym- 
pathetic trunk  and  its  relation  with  the  spinal  nerves  and  with  the  per- 
ipheral sympathetic  ganglionated  plexuses;  cf.  Fig.  41,  p.  107.  (After 
Schwalbe.) 


THE    SYMPATHETIC    NERVOUS    SYSTEM  227 

sympathetic  system  includes  those  neurons  which  put  the  periph- 
eral autonomous  system  into  functional  connection  with  the 
central  nervous  system,  thus  providing  a  central  regulatory  con- 
trol over  the  autonomous  system.  This  part  of  the  sympa- 
thetic nervous  system  includes  the  peripheral  courses  of  the 
neurons  involved  in  the  general  cerebrospinal  visceral  reflex  sys- 
tems (see  pp.  76,  89,  93). 

The  peripheral  autonomous  nervous  system  appears  to  be  a 
direct  survival  of  that  diffuse  type  of  nervous  system  which  is 
found  in  the  lowest  animals  which  possess  nerves  at  all,  such  as 
some  jelly-fishes  and  worms.  The  central  nervous  system  of 
higher  animals  is  supposed  to  have  developed  by  a  concentration 
of  ganglia  in  such  a  diffuse  system  (see  p.  27),  a  portion  of  which 
remains  as  the  peripheral  autonomous  sympathetic  system  (Fig. 
17,  p.  53).  But  during  evolution  the  central  nervous  system 
increased  in  importance  for  integrating  and  regulating  the 
functions  of  the  body,  the  central  control  of  the  viscera  assumed 
greater  importance,  and  the  general  cerebro-spinal  visceral  sys- 
tems were  developed  to  serve  this  function. 

Figure  56  (p.  126)  illustrates  the  typical  arrangement  of  the 
visceral  sensory  and  motor  fibers  in  the  spinal  nerves,  and  their 
relations  to  the  sympathetic  ganglia  and  nerves.  These  fibers, 
of  course,  belong  to  the  cerebro-spinal  visceral  systems;  the 
peripheral  autonomous  system  is  not  included  in  the  diagram. 
The  central  control  of  the  visceral  apparatus  is  effected  (1)  by 
afferent  visceral  nerve-fibers  distributed  peripherally  through 
the  sympathetic  nerves  and  entering  the  spinal  cord  through  the 
dorsal  spinal  roots,  and  (2)  by  efferent  visceral  nerves  which 
leave  the  spinal  cord  through  the  ventral  roots  and  also  enter  the 
sympathetic  nerves.  In  lower  vertebrates  (and  possibly  also  in 
man)  some  of  these  fibers  leave  by  the  dorsal  roots  also. 

The  cell  bodies  of  the  afferent  neurons  lie  in  part  in  the 
spinal  ganglia  and  in  part  in  the  sympathetic  ganglia.  Figure 
109  illustrates  the  connections  of  these  two  types  of  afferent 
visceral  neurons.  Neuron  3  of  this  figure  may  transmit  its 
impulse  either  directly  into  the  spinal  cord  through  its  centrally 
directed  process  or  by  a  collateral  branch  to  some  other  cell 
body  of  the  spinal  ganglion  (neuron  1).  The  fiber  marked  4 
arises  from  a  cell-body  lying  in  some  sympathetic  ganglion  and 


228 


INTRODUCTION   TO   NEUROLOGY 


terminates  in  synaptic  relation  with  some  neuron  whose  cell 
body  lies  in  the  spinal  ganglion,  which,  in  turn,  may  transmit  this 
visceral  impulse  into  the  spinal  cord  in  addition  to  its  own  proper 
function,  say,  of  cutaneous  sensibility. 


sDinal  ganglion 


peripheral 
nerve 


Fig.  109. — Diagram  illustrating  three  ways  in  which  afferent  visceral 
fibers  may  connect  with  the  central  nervous  system  through  the  spinal 
ganglia  (cf.  Fig.  56,  p.  126).  Neurons  1  and  2  are  typical  somatic  sensory 
neurons,  whose  peripheral  fibers  reach  the  skin.  Neuron  3  is  a  visceral 
sensory  neuron,  whose  peripheral  fiber  enters  the  sympathetic  nervous  sys- 
tem through  the  communicating  branch  (this  neuron  is  drawn  in  fine  dotted 
fines  in  Fig.  56).  Neurons  of  the  third  type  may  bring  in  afferent  impulses 
from  the  viscera  through  their  peripheral  processes  and  transmit  these  im- 
pulses directly  to  the  spinal  cord  through  their  central  processes.  A  col- 
lateral branch  from  this  neuron,  moreover,  may  carry  the  visceral  impulse 
to  the  cell  body  of  a  neuron  of  type  1,  which  thus  serves  to  convey  both 
somatic  impulses  from  the  skin  and  visceral  impulses  from  some  deep-seated 
organ.  The  spinal  ganglion  also  receives  nerve-fibers  of  the  type  marked  4, 
whose  cell  bodies  lie  in  the  sympathetic  ganglia.  These  probably  convey 
visceral  afferent  impulses  as  far  as  the  spinal  ganglion,  which  are  then  trans- 
mitted to  the  spinal  cord  through  a  somatic  sensory  neuron.  These  arrange- 
ments are  described  in  detail  by  Dogiel. 

The  relations  just  described  probably  provide  the  neurological 
mechanism  of  some  of  the  curious  phenomena  known  as  referred 
pains.  It  is  well  known  that  disease  of  certain  internal  organs 
may  be  accompanied  by  no  pain  at  the  site  of  the  injury,  but  by 
cutaneous  pain  and  tenderness  in  remote  parts  of  the  body. 
Fig.  110  illustrates  some  of  these  areas  of  referred  pain  and  the 


THE    SYMPATHETIC    NERVOUS    SYSTEM  229 

sources  of  the  excitations.  The  mechanisms  shown  in  Fig. 
109  show  how  an  inflammatory  process  or  other  injury  of  the 
sympathetic  nerves  associated  with  these  deep  viscera  may  read- 
ily be  carried  over  to  the  related  neurons  of  the  somatic  sensory 
system.  Many  referred  pains  are  undoubtedly  due  to  similar 
collocations  of  visceral  and  somatic  sensory  paths  within  the 
spinal  cord  and  brain.  Since  the  functions  of  these  visceral 
nerves  do  not  usually  come  into  consciousness  at  all,  the  pain 
will  be  referred  to  the  peripheral  area  of  distribution  of  the 
associated  somatic  nerve,  which  has  a  distinct  "local  sign,"  or 
habitual  peripheral  reference. 

The  efferent  fibers  of  the  cerebro-spinal  visceral  system  arise 
from  several  groups  of  cells  in  the  intermediate  zone  between 
the  dorsal  and  ventral  gray  columns  of  the  spinal  cord,  and  in 
particular  from  an  intermedio-lateral  column  of  cells  at  the  mar- 
gin of  the  lateral  column  of  gray  matter  (Fig.  56,  p.  126).  These 
efferent  fibers  never  reach  their  peripheral  terminations  directly. 
They  always  end  in  some  sympathetic  ganglion,  either  of  the 
vertebral  ganglionic  trunk  or  one  of  the  peripheral  sympathetic 
ganglia.  Here  there  is  a  synapse,  and  a  second  neuron  of  the 
sympathetic  ganglion  in  question  takes  up  the  nervous  impulse 
and  transmits  it  to  its  termination  in  some  unstriated  visceral 
muscle  or  gland.  The  efferent  fiber  arising  from  a  cell  body 
within  the  spinal  cord  is  termed  the  preganglionic  fiber,  and  the 
peripheral  fiber  arising  from  a  neuron  of  the  sympathetic  gang- 
lion is  the  postganglionic  fiber.  The  former  is  usually  a  small 
myelinated  fiber;  the  latter  is  usually  unmyelinated.  The  pre- 
ceding description  is  applicable  to  the  visceral  nervous  sj^stem 
in  the  trunk  region  of  the  body.  In  the  head  the  connections 
of  the  nerves  of  this  type  are  much  more  complex. 

Langley  and  others  have  shown  that  what  is  here  termed  the 
general  cerebro-spinal  visceral  system  is  related  to  four  distinct 
regions  of  the  central  nervous  system,  as  illustrated  by  Fig.  111.^ 

^  Langley  calls  the  entire  sympathetic  system  the  autonomic  system,  and 
limits  the  application  of  the  term  "sympathetic"  to  what  is  here  called  the 
thoracic-lumbar  sympathetic.  There  is  no  adequate  ground  for  his  belief 
that  the  latter  is  genetically  different  from  the  other  parts  of  the  cerebro- 
spinal visceral  apparatus,  though  its  jihysiological  characteristics  are  very 
distinctive.  Many  of  the  viscera  have  a  double  innervation  through  the  sym- 
pathetic, one  set  of  fibers  coming  from  the  midbrain,  bulbar,  or  sacral  sym- 
pathetic ganglia  and  an  antagonistic  set  coming  from  the  thoracic-lumbar 
sympathetic  gangUa. 


230 


INTRODUCTION  TO   NEUROLOGY 


Aruemia 

Endometritis 

Bladder? 

,J-^Decnycd  teeth 

^     ~/~J''-'--  Pharyngitis 
^  ^^•■''  Otitis  media 


tleurastheni 
(^spinal  irritation ) 


Sroad  ligaments 
and  ovaries 


Litha 
'  Neurasthenia 
Ovai'iest 


Fig.  110. — The  locations  of  referred  pains  and  their  causes, 
from  Starr's  Nervous  Diseases.) 


(After  Dana, 


Area,  cerebrospinal 
nerves. 

I.  Trigeminus,    fa- 
cial. 
II.  Upper  cendcal. 

III.  Lower  four  cer- 

vical   ancf   first 
thoracic. 

IV.  Upper   six  thor- 

acic. 
V.  Lower  six  thor- 
acic. 

VI.  Twelfth   thoracic 

and  fourth  lum- 
bar. 

VII.  Fifth  lumbar  and 

five  sacral. 


Distribution. 
Face  and  anterior 

scalp. 
Occiput,  neck. 
Upper  extremity. 


Thorax. 

Abdomen,  upper 
lumbar. 

Lumbar,  upper 
gluteal,  anterior 
thigh,  and  knee. 

Lower  gluteal, 
posterior  thigh 
and  leg. 


Associated  ganglia 
of  sympathetic. 

Four  cerebral. 

First  cervical. 
Second  and  third 

cervical,     first 

thoracic. 
First     to      sixth 

thoracic. 
Sixth  to  twelfth 

thoracic. 

First      to      fifth 
lumbar. 

First      to      fifth 
sacral. 


Distribution. 
Head. 

Head,  ear. 
Heart. 


Lungs. 

Viscera  of  ab- 
domen and 
testes. 

Pelvic  or- 
gans. 

Pelvic  or- 
gans and 
legs. 


THE    SYMPATHETIC    NERVOUS    SYSTEM  231 

The  portions  of  the  sympathetic  system  related  to  these  respec- 
tive regions  are  as  follows:  (1)  The  midbrain  sympathetic,  com- 
prising chiefl}^  the  ciliary  ganglion  behind  the  eye  and  its  nerves, 
these  being  related  to  the  brain  through  the  III  cranial  nerve. 
(2)  The  bulbar  sympathetic,  related  to  the  brain  chiefly  through 
the  VII,  IX,  and  X  cranial  nerves.  (3)  The  thoracic-lumbar 
sympathetic,  related  to  the  spinal  cord  through  the  I  thoracic 
to  II  or  III  lumbar  nerves.  (4)  The  sacral  sympathetic, 
related  to  the  spinal  cord  through  the  II  to  IV  sacral  nerves. 

Each  of  these  four  regions  has  its  own  distinctive  physiological 
characteristics,  including  in  some  cases  a  special  type  of  reaction 
to  certain  drugs.  They  all  exhibit  a  common  reaction  to  nico- 
tin  in  physiological  doses.  The  effect  of  this  poison  is  to  paralyze 
the  synapses  between  the  preganglionic  and  the  postganglionic 
neurons  and  thus  to  isolate  the  peripheral  sympathetic  neurons 
physiologically  from  efferent  impulses  arising  within  the  central 
nervous  system.  Adrenalin  (extract  of  the  suprarenal  glands) 
affects  chiefly  the  thoracic-lumbar  sympathetic  system  (see  p. 
255).  On  the  other  hand,  poisons  of  a  different  group,  including 
atropin,  muscarin,  and  pilocarpin,  are  said  to  act  chiefly  upon 
the  midbrain,  bulbar  and  sacral  sympathetic,  but  not  upon  the 
thoracic-lumbar  system.  There  are  other  cases  of  very  specific 
action  of  drugs  upon  special  parts  of  the  sympathetic  nervous 
system. 

Summary. — From  the  preceding  considerations  it  is  evident 
that  the  sympathetic  nervous  system  cannot  be  sharply  sepa- 
rated anatomically  or  phj^siologically  from  the  cerebro-spinal 
system.  The  cell  bodies  of  the  neurons  of  the  cerebro-spinal 
visceral  system  lie  partly  within  and  partly  without  the  central 
nervous  axis.  A  ganglionic  sympathetic  trunk  extends  on  each 
side  of  the  body  along  the  spinal  column,  and  the  ganglia  of  this 
trunk  are  connected  with  most  of  the  spinal  nerves  by  com- 
municating branches.  The  neurons  of  this  trunk  of  vertebral 
sympathetic  ganglia  belong  chiefly  to  the  cerebro-spinal  visceral 
system,  since  they  are  concerned  with  the  central  regulatory 
mechanism  of  the  viscera.  All  parts  of  the  visceral  nervous  sys- 
tem which  lie  peripherally  of  the  communicating  branches 
between  the  sympathetic  ganglionated  trunks  and  the  spinal 
roots,  and  can  be  anatomically  separated  from  the  peripheral 


232 


INTRODUCTION   TO   NEUROLOGY 


Sphincter  of  iris  ] 
Ciliary  muscle  J 

Heart,  blood-vessels  of  mucous  mem-1 
branes  of  head,  salivary  glands,  walls  of  1 
digestive  tract  from  mouth  to  descending  I 
colon,  including  outgrowths  of  this  re-  ( 
gion — trachea  and  lungs,  gastric  glands,  | 
liver,  pancreas.  J 


a  Midbrain  sympathetic 


Bulbar  sympathetic 


Dilator  of  iris,  orbital  muscles,  arteries,  ) 
muscles  and  glands  of  the  skin,  blood-  I 
vessels  of  lungs  and  abdominal  viscera  and  | 
of  digestive  tract  between  mouth  and  rec-  )■ 
tum,  arteries  of  skeletal  muscles,  muscles  I 
of  spleen,  ureter,  and  internal  generative  | 
organs.  J 


Arteries  of  rectum,  anus,  and  external "" 
generative  organs,  muscles  of  external  gen- 
erative   organs,    walls    of    bladder    and 
urethra,  walls  of  descending  colon  to  aniis.  j 


J  Thoracic-lumbar  sympathetic 
(I  thoracic  to  11  or  III  lumbar 


/Sacral  sympathetic 
I^II  to  IV  sacral 


Fig.  111. — Diagram  of  the  central  localization  of  the  cerebro-spinal  visceral 
nervous  connections.     (Modified  from  Langley.) 


THE    SYMPATHETIC    NERVOUS    SYSTEM  233 

branches  of  the  cerebro-spinal  nerves,  are  commonly  described 
as  constituting  the  sympathetic  nervous  system.  This  system 
includes  the  ganglionated  trunks  bordering  the  spinal  column, 
to  which  reference  has  just  been  made,  the  larger  peripheral 
ganglionated  plexuses  of  the  head,  thorax,  and  abdomen,  and  a 
very  large  number  of  minute  sympathetic  ganglia  scattered 
everywhere  throughout  the  body.  This  sympathetic  nervous 
system  we  have  regarded  as  composed  of  two  imperfectly 
separable  parts:  (1)  a  series  of  autonomous  peripheral  ganglia  for 
the  local  regulation  of  the  organs  within  which  they  are  found; 
(2)  the  neurons  of  the  cerebro-spinal  visceral  systems  which  en- 
able the  central  nervous  system  to  maintain  a  regulatory  control 
over  the  intrinsic  autonomous  systems. 

Literature 

DoGiEL,  A.  S.  1908.  Der  Bau  der  Spinalganglien  des  Menschen  und  der 
Siiugetiere,  Jena,  G.  Fischer,  151  pp.,  14  plates. 

Head,  H.  1893.  On  Disturbances  of  Sensation  with  Especial  Reference 
to  the  Pain  of  Visceral  Disease,  Brain,  vol.  xvi,  pp.  1-133. 

— .  1901.  The  Gulstonian  Lectures  for  1901,  Brain,  vol.  xxiv,  p.  398. 

Head  and  Campbell.  1901.  Pathology  of  Herpes  Zoster,  Brain,  vol. 
xxiii,  p.  353. 

Huber,  G.  C.  1897.  Lectures  on  the  Sympathetic  Nervous  System, 
Jour.  Comp.  Neur.,  vol.  vii,  pp.  73-145. 

KuNTZ,  A.  1911.  The  Evolution  of  the  Sympathetic  Nervous  System  in 
Vertebrates,  Jour.  Comp.  Neur.,  vol.  xxi,  pp.  215-236. 

Langley,  J.  N.  1900.  The  Sjonpathetic  and  Other  Related  Systems  of 
Nerves,  in  Schaefer's  Text-book  of  Physiology,  London,  pp.  616-696. 

— .  1900.  On  Axon-reflexes  in  the  Preganglionic  Fibers,  Jour,  of  Physiol., 
vol.  xxv,  p.  364. 

— .  1903.  The  Autonomic  Nervous  System,  Brain,  vol.  xxvi,  pp.  1-26. 

Onuf,  B.,  and  Collins,  J.  1900.  Experimental  Researches  on  the  Central 
Locahzation  of  the  Sympathetic  with  a  Critical  Review  of  its  Anatomy  and 
Physiology,  Archives  of  Neurology  and  Psychopathology,  vol.  iii,  p.  1-252. 


CHAPTER  XVII 

THE   VISCERAL   AND    GUSTATORY   APPARATUS 

Our  knowledge  of  the  functional  localization  within  the  spinal 
cord  of  the  general  visceral  reflex  centers  related  to  the  spinal 
nerves  is  still  rather  indefinite.  Most  of  the  cerebro-spinal 
control  of  the  visceral  reactions  of  the  body  is  effected  from  the 
bulbar  sympathetic  centers  by  way  of  the  vagus  nerve.  The 
afferent  fibers  of  these  systems  all  enter  the  fasciculus  solitarius, 
a  longitudinal  bundle  of  fibers  in  the  lower  part  of  the  medulla 
oblongata,  and  they  terminate  in  the  nucleus  of  visceral  sensory 
neurons  which  accompanies  this  fasciculus  (Figs.  71-74,  77, 
114).  The  special  visceral  fibers  of  the  nerves  of  taste  also  ter- 
minate in  this  nucleus.  The  efferent  fibers  of  these  systems  arise 
chiefly  from  the  dorsal  motor  nucleus  of  the  vagus,  a  cluster  of 
neurons  which  produces  an  eminence  in  the  floor  of  the  fourth 
ventricle  known  as  the  ala  cinerea  or  trigonum  vagi  (Figs.  71- 
74,  114).  From  this  nucleus  arise  preganglionic  fibers  for  the 
innervation  of  various  systems  of  visceral  muscles  of  blood- 
vessels, esophagus,  stomach,  intestine,  bronchi,  and  others. 

Most  viscera  possess  a  double  innervation — from  the  thoracic- 
lumbar  sympathetic  system  and  from  the  midbrain,  bulbar,  or 
sacral  system  (see  p.  229).  For  instance,  the  heart-beat  is 
accelerated  by  the  thoracic-lumbar  system  and  inhibited  by  the 
bulbar  system  through  the  vagus;  and  the  iris  is  contracted 
through  the  midbrain  sympathetic,  but  dilated  through  the 
thoracic  by  way  of  the  superior  cervical  ganglion  (p.  211). 

Organs  of  Circulation. — The  nervous  control  of  the  heart 
and  blood-vessels  is  far  too  complex  for  full  description  here.  A 
few  general  features  only  can  be  touched  upon. 

The  rate  of  blood  flow  may  be  varied  for  the  body  as  a  whole 
by  changes  in  the  rate  and  force  of  the  pulsations  of  the  heart, 
and  for  particular  parts  of  the  body  by  changes  in  the  caliber 
of  its  blood-vessels.     The  heart  beats  automatically,  but  its 

234 


THE    VISCERAL    AND    GUSTATORY    APPARATUS  235 

rate  is  regulated  through  the  cardiac  nerves.  The  cahber  of 
the  smaller  blood-vessels  and  hence  the  amount  of  blood  which 
can  pass  through  them  is  regulated  by  vasomotor  nerves.  Both 
the  heart  and  the  muscular  walls  of  the  vessels  have  a  double 
innervation.  The  heart  has  an  accelerator  nerve  and  an  in- 
hibitory nerve;  the  smaller  arteries  have  vasodilator  and  vaso- 
constrictor nerves.  The  amount  of  blood  pumped  by  the  heart 
at  any  time  will  depend  upon  the  equilibrium  existing  between 
its  accelerator  and  its  inhibitory  fibers  and  upon  the  resist- 
ance offered  by  the  peripheral  vessels;  that  flowing  through 
any  particular  system  of  blood-vessels  will  be  affected  also  by 
the  equiUbrium  between  the  vasodilator  and  the  vasoconstrictor 
nerves  of  these  vessels. 

There  are  sympathetic  ganglia  within  the  heart.  Its  extrinsic 
nerve  supply  includes  afferent  fibers  to  the  brain  and  efferent 
fibers  of  two  sorts,  viz.,  the  accelerator  and  inhibitory  fibers 
already  mentioned.  The  afferent  fibers  are  represented  in  a 
small  sympathetic  nerve,  the  nerve  of  Cyon,  which  is  also  called 
the  depressor  nerve.  They  arise  from  the  walls  of  the  ventricles 
of  the  heart  and  join  the  vagus  trunk,  through  which  they  enter 
the  medulla  oblongata.  Stimulation  of  this  nerve  produces  a  fall 
of  arterial  pressure  by  dilating  the  vessels  throughout  the  body, 
especially  in  the  viscera.  It  appears  to  act  to  reduce  the  labor 
of  the  heart  when  intraventricular  pressure  becomes  excessive. 

The  medulla  oblongata  contains  a  center  whose  stimulation 
causes  inhibition  of  the  heart-beat.  These  efferent  fibers  go  out 
as  preganglionic  fibers  of  the  vagus  nerve  and  terminate  in  the 
cardiac  sympathetic  plexus  (Fig.  108),  where  their  postganglionic 
neurons  are  located.  There  is  also  a  center  in  the  medulla  ob- 
longata (which  has  not  been  precisely  localized)  whose  stimula- 
tion causes  acceleration  of  the  heart-beat.  These  accelerator 
nerve-fibers  do  not  leave  the  brain  through  the  vagus,  but  appar- 
ently they  descend  through  the  spinal  cord  to  the  lower  cervical 
region  and  pass  out  into  the  sympathetic  nervous  sj'stem  at  this 
level.  The  centers  of  vasomotor  control  of  various  regions  of 
the  body  are  indicated  in  Fig.  111. 

Organs  of  Respiration. — Oxygen  is  supplied  to  the  tissues  of 
the  body  in  a  great  variety  of  ways  in  different  animals.  In 
some  of  the  simpler  animals,  as  in  plants  generally,  oxygen  is 


236  INTRODUCTION  TO  NEUROLOGY 

simply  absorbed  from  the  surrounding  medium  by  the  exposed 
surfaces.  In  all  but  the  lowest  animals  there  is  a  blood-vascular 
system  by  means  of  which  the  oxygen  absorbed  at  the  surface  is 
transferred  to  the  deeper  tissues.  In  insects,  however,  this  re- 
sult is  obtained  chiefly  by  a  different  apparatus,  namely,  a  sys- 
tem of  air  tubes  (tracheas)  which  ramify  among  the  tissues  and 
supply  oxygen  directly  to  the  functioning  cells.  In  most  water- 
breathing  animals  a  portion  of  the  surface  of  the  body  is  lamel- 
lated  and  vascularized  to  form  gills  to  facilitate  the  absorption  of 
oxygen  by  the  blood-stream,  and  in  air-breathing  vertebrates 
lungs  are  developed  to  accomplish  the  same  result.  The  nervous 
mechanisms  of  respiration  will  differ  in  all  of  the  cases  cited 
above,  and  it  is  only  in  mammals  that  we  shall  here  consider  the 
details  of  this  mechanism. 

In  ordinary  breathing,  inspiration  is  effected  by  actively  in- 
creasing the  volume  of  the  thoracic  cavity  and  thus  creating  a 
suction  through  the  trachea,  while  expiration  is  the  result  of  the 
passive  return  of  the  organs  involved  to  their  former  positions 
by  reason  of  their  own  elasticity.  The  muscles  involved  in 
inspiration  belong  to  two  groups:  (1)  the  internal  apparatus,  i.  e., 
the  diaphragm,  and  (2)  the  external  apparatus,  the  intercostal 
and  other  muscles  of  the  body  wall.  These  are  all  somatic 
muscles.  In  forced  respiration  various  other  muscles  act  in  an 
accessory  way  during  both  inspiration  and  expiration. 

The  diaphragm  is  innervated  by  the  phrenic  nerve,  which 
takes  its  origin  from  the  fourth  and  fifth  cervical  spinal  nerves; 
and  the  intercostal  muscles  are  innervated  by  ventral  spinal 
roots  arising  successively  from  all  thoracic  segments  of  the  spinal 
cord  (Fig.  112).  The  accessory  muscles  are  in  part  somatic 
muscles  of  the  abdomen  and  shoulder  and  in  part  special  vis- 
ceral muscles  of  the  head,  particularly  those  of  the  glottis 
(innervated  by  the  vagus)  and  of  the  nostrils  (innervated  by  the 
VII  cranial  nerve). 

The  anatomical  relations  just  described  imply  that,  although 
respiration  is  a  visceral  function,  in  mammals  the  necessary 
movements  for  ordinary  breathing  are  performed  by  somatic 
muscles.  This  is  not  true  in  fishes.  Here  the  organs  of  respi- 
ration (gills)  are  strictly  visceral  structures  innervated  by  vis- 
ceral components  of  the  cranial  nerves,  whose  cerebral  center  is 


THE    VISCERAL    AND    GUSTATORY    APPARATUS 


237 


in  the  lower  part  of  the  medulla  oblongata  (the  area  visceralis  of 
Fig.  43,  p.  111). 

In  the  ordinary  breathing  of  mammals  the  act  of  inspiration 
is  effected  by  an  upward  and  outward  movement  of  the  ribs  and 
a  downward  movement  of  the  cUaphragm.  Now,  if  the  spinal 
cord  be  cut  through  at  the  level  of  the  seventh  cervical  nerve  the 
respiratory  movement  of  the  ribs  is  entirely  abolished,  though 
the  movements  of  the  diaphragm  go  on  as  usual.    The  continuity 


Dorsal  motor  X 

nucleus 
Nucleus  of  fascic.  solitarius 

Fasciculus  solitarius 

Vagus  ganglion 

Vagus  nerve 

Tr.  solitario-spinalis 

Sympathetic  ganglion 


Lung- 
Intercostal  nerve. 

Intercostal  muscl 
Phrenic  nerve 


Respiratory  center 


Diaphragm 


Fig.  112. — Diagram  of  the  nervous  mechanism  of  respiration, 
from  Ramon  y  Cajal.) 


(Modified 


of  the  thoracic  motor  nerves  which  innervate  the  intercostal 
muscles  with  their  centers  of  origin  in  the  spinal  cord  is  undis- 
turbed by  this  operation,  yet  they  can  no  longer  be  coordinated 
in  the  respiratory  act.  If  in  another  animal  the  spinal  cord  be 
divided  at  the  level  of  the  third  cervical  nerve,  i.  e.,  above  the 
level  of  origin  of  the  phrenic  nerve,  the  respiratory  movements  of 
both  the  ribs  and  the  diaphragm  cease,  even  though  the  spinal 
cord  below  the  section  is  intact  and  its  connection  with  the 
peripheral  respiratory  apparatus  is  undisturbed.     These  experi- 


238  INTRODUCTION   TO   NEUROLOGY 

ments  show  that  the  spinal  segments  from  which  all  of  the  motor 
respiratory  nerves  arise  cannot  of  themselves  effect  the  coor- 
dinations necessary  in  respiration.  This  is  in  marked  contrast 
with  many  other  reactions  (both  visceral  and  somatic),  whose 
performance  is  still  possible  after  the  separation  of  the  spinal 
cord  from  the  brain. 

If  now,  in  a  third  animal,  the  medulla  oblongata  is  cut  across 
at  any  point  above  the  middle  of  its  length,  say  at  the  lower  bor- 
der of  the  pons,  the  respiratory  processes  are  in  no  way  disturbed. 
This  shows  that  there  is  a  respiratory  correlation  center  in  the 
lower  half  of  the  medulla  oblongata,  that  is,  somewhere  in 
the  region  corresponding  to  the  "visceral  area"  of  the  fish 
brain. 

The  air  tubes  of  the  lungs  are  provided  with  smooth  muscle- 
fibers  by  which  their  cahber  may  be  contracted.  These  muscles 
are  innervated  by  the  vagus,  and  the  hyperexcitation  of  their 
motor  nerves  may  impede  respiration,  this  being  one  of  the  fac- 
tors which  cause  asthma.  The  cerebral  center  from  which  these 
intrinsic  muscles  of  the  lungs  are  innervated  has  been  shown  to 
lie  in  the  middle  part  of  the  dorsal  motor  vagus  nucleus  (Fig.  73, 
nuc  dorsalis  vagi).  These  are  preganglionic  neurons,  the  cor- 
responding postganglionic  neurons  lying  in  sympathetic  ganglia 
distributed  along  the  pulmonary  branches  of  the  vagus  (Fig.  112). 

The  apparatus  described  in  the  preceding  paragraph  is,  how- 
ever, not  responsible  for  the  maintenance  of  the  regular  rhythm 
of  breathing.  Physiological  experiments  show  that  there  is  some- 
where in  the  lower  part  of  the  medulla  oblongata  a  respiratory 
center  which  performs  this  function.  This  center  may  appa- 
rently be  excited  to  activity  directly  by  variations  in  the  compo- 
sition of  the  blood  which  reaches  it,  especially  either  by  a  de- 
ficiency in  oxygen  or  by  an  excess  of  carbon  dioxid.  Its  activity 
may  also  be  modified  by  nervous  influences  reaching  it  through 
the  peripheral  afferent  nerves,  the  vagus  being  the  only  nerve 
which  appears  to  be  able  to  act  directly  on  the  respiratory  center, 
though  the  strong  excitation  of  almost  any  sensory  nerve  of  the 
body  may  under  some  circumstances  indirectly  affect  the  res- 
piratory rhythm.  Coughing  and  sneezing  are  special  cases  of 
this  sort.  The  reflex  mechanism  of  the  cough  is  illustrated  in 
Fig.  113. 


THE    VISCERAL    AND    GUSTATORY    APPARATUS 


239 


Vagiis 
ganglion 


LarjTis- 


Stomach 


Sympathetic 

ganglion 
Postgangli- 
onic neuron 


Fig.  113. — Diagram  of  the  nervous  mechanisms  of  coughing  and  vomit- 
ing. In  the  cough  an  irritation  of  the  mucous  membrane  of  the  larynx  is 
transmitted  to  the  nucleus  of  the  fasciculus  sohtarius,  from  which  the 
tractus  soUtario-.spinalis  passes  downward  to  the  motor  centers  of  the  spinal 
cord  for  the  innervation  of  the  muscles  of  the  diaphragm,  the  abdominal 
wall,  and  the  ribs  which  cooperate  in  the  production  of  the  cough.  In 
vomiting,  an  irritation  of  the  stomach  is  carried  by  sensory  fibers  of  the 
vagus  to  the  nucleus  of  the  fasciculus  solitarius,  from  which  the  pathway  is 
as  before  to  the  spinal  motor  centers  for  the  innervation  of  the  diaphragm 
and  abdominal  wall.  In  this  case  there  is  also  an  excitation  of  the  dorsal 
motor  vagus  nucleus,  from  which  preganglionic  fibers  go  out  into  the  vagus 
nerve  for  a  sympathetic  ganglion  in  the  h^-poga-tric  plexus,  from  which, 
in  turn  postgangUonic  fibers  pass  to  the  muscles  of  the  stomach  which  par- 
ticipate in  the  ejection  of  its  contents.  The  diagram  is  suggested  by  one 
in  Ramon  y  Cajal's  text-book^  though  greatly  modified. 


Attempts  to  locahze  the  respiratory  center  in  the  mammalian  medulla 
oblongata  more  accurately  have  led  to  contradictory  results.     The  old 


240  INTRODUCTION  TO  NEUROLOGY 

conception  of  Flourens  that  there  is  a  minute  "  vital  node"  under  the  lowest 
point  of  the  fourth  ventricle  which  is  the  respiratory  center  must  be  aban- 
doned. Later  the  fasciculus  solitarius  was  identified  as  the  "respiratory 
tract,"  and  the  nucleus  associated  with  this  tract  was  regarded  as  the 
respiratory  center,  but  further  experiment  has  shown  that  this  is  not  an 
exact  statement  of  the  case.  Some  physiological  experiments  have  sug- 
gested that  the  respiratory  rhythm  is  maintained  by  a  center  in  the 
reticular  formation  of  the  vagus  region  ventrally  of  the  fasciculus  solitarius. 

It  has  recently  been  shown,  as  stated  above,  that  afferent  visceral  fibers 
from  the  lungs  whose  cell  bodies  he  in  the  vagus  ganglion  enter  the  fascicu- 
lus solitarius,  and  it  is  known  that  from  the  nucleus  of  this  tract  a  "tractus 
solitario-spinahs "  (Fig.  112)  descends  into  the  motor  centers  of  the  upper 
segments  of  the  spinal  cord.  This  descending  visceral  spinal  tract  probably 
plays  some  part  in  the  regulation  of  respiration,  though  not  the  chief  role. 
Ramon  y  Cajal  and  Kappers  beheve  that,  while  the  upper  part  of  the  nucleus 
of  the  fasciculus  sohtarius  has  nothing  to  do  with  respiration,  the  lower  end 
of  this  nucleus  (commissural  nucleus  of  Cajal,  see  Figs.  71, 112,  and  114)  is  a 
true  respiratory  center.  Ramon  y  Cajal,  in  fact,  thinks  that  this  nucleus 
serves  both  for  reflexes  excited  by  the  sensory  pulmonary  nerves  and  also  for 
the  normal  respiratory  rhythm  excited  by  carbon  dioxid  in  the  blood. 
This  hypothesis  is  not  supported  by  direct  physiological  experiment,  and  for 
the  present  we  must  content  oiuselves  with  the  statement  that  the  true 
respiratory  center  has  not  been  accurately  located  anatomically.  Figure 
112  may  be  regarded  as  a  true  pictiue  of  the  essential  relations  of  the 
respiratory  nerves,  with  the  reservation  that  the  position  of  the  respiratory 
center  is  not  precisely  known.  . 

There  is  also  a  reflex  center  for  the  regulation  of  respiration  in  the  medial 
wall  of  the  thalamus  and  others  have  been  described  in  different  parts  of  the 
brain  stem.  The  entire  respiratory  mechanism  is  also  under  partial  volun- 
tary control  from  the  cerebral  cortex. 

While  many  features  of  the  central  respiratory  mechanism 
remain  obscure,  it  seems  evident  that  the  location  of  the  chief 
respiratory  center  in  the  "visceral  area"  of  the  lower  part  of  the 
medulla  oblongata  instead  of  the  portions  of  the  spinal  cord 
directly  connected  with  the  respiratory  muscles  is  a  survival  of 
the  ancestral  condition  found  in  fishes,  where  the  entire  respira- 
tory function  is  carried  on  by  a  visceral  apparatus  (gills)  inner- 
vated from  the  vagus  region. 

Organs  of  Digestion.— Hunger  seems  to  be  a  complex  in  which 
at  least  three  factors  are  present:  (1)  Specific  hunger  pangs  due 
to  waves  of  muscular  contraction  in  the  stomach  (Cannon, 
Carlson) ;  (2)  appetite,  or  craving  for  food  regardless  of  the  state 
of  the  stomach;  (3)  general  malaise  from  starvation  of  the  tissues 
and  weakness.  Appetite  may  persist  after  section  of  the  vagus 
nerves  and  is  probably  a  sensation  distinct  from  the  hunger 
pangs. 


THE    VISCERAL    AND    GUSTATORY    APPARATUS  241 

The  ordinary  processes  of  digestion  are  carried  on  partly  by 
automatic  activities  of  the  organs  without  nervous  control 
(see  p.  224),  and  partly  by  the  intrinsic  sympathetic  nervous 
system  of  the  digestive  organs.  Throughout  the  length  of  the 
digestive  tract  there  are  two  sympathetic  ganglionated  plexuses. 
One  of  these  is  located  between  the  muscular  coats  of  the  stom- 
ach and  intestine,  known  as  the  myenteric  or  Auerbach's  plexus; 
the  other  lies  immediately  under  the  lining  mucous  membrane 
and  is  known  as  the  submucous  or  Meissner's  plexus.  It  has 
been  shown  physiologically  that  the  local  reflexes  concerned  in 
the  typical  peristaltic  contractions  of  the  digestive  tube  are 
effected  chiefly  by  the  myenteric  plexus.  Accordingly,  this 
reflex  is  called  by  Cannon  the  myenteric  reflex. 

The  entire  digestive  mechanism  (like  most  of  the  other  visceral 
systems)  may  also  be  influenced  indirectly  by  nervous  impulses 
arising  in  the  cerebral  cortex,  though  these  organs  are  not  under 
direct  voluntary  control.  It  is  well  known  that  the  digestive 
processes  are  especially  sensitive  to  emotional  states,  pleasurable 
experiences  promoting  digestion  and  painful  or  disagreeable  emo- 
tions inhibiting  it.  These  facts  can  be  studied  on  laboratory  ani- 
mals under  experimental  conditions  (Cannon) .  A  large  amount 
of  information  regarding  the  physiology  of  digestion  has  recently 
been  gathered  by  Carlson  from  the  study  of  a  man  with  an  arti- 
ficial opening  into  the  stomach  (gastric  fistula),  permitting 
direct  observation  of  the  stomach  at  all  times. 

The  salivary  glands  are  excited  to  secretion  from  two  nuclei 
of  the  medulla  oblongata,  the  superior  salivatory  nucleus  (Figs. 
71,  114),  whose  preganglionic  fibers  go  out  with  the  VII  cranial 
nerve  for  the  sublingual  and  submaxillary  salivary  glands,  and 
the  inferior  salivatory  nucleus  (Figs.  71,  73,  114),  whose  fibers 
go  out  with  the  IX  nerve  for  the  parotid  gland.  The  secretion 
of  saliva  may  be  produced  either  as  a  simple  reflex  from  the 
presence  of  food  in  the  mouth  through  the  gustatory  nerves  and 
fasciculus  solitarius,  or  as  so-called  psychic  secretion  excited  by 
the  sight  or  thought  of  food.  All  of  the  digestive  secretions 
are  susceptible  to  this  sort  of  indirect  excitation,  as,  indeed,  are 
most  other  processes  which  are  under  the  control  of  the  cerebro- 
spinal visceral  nervous  system.  These  visceral  reactions,  in 
their  turn,  are  reported  back  to  the  central  nervous  system  and 

16 


242  INTRODUCTION  TO  NEUROLOGY 

no  doubt  play  a  very  large  part  in  shaping  the  organic  back- 
ground of  the  entire  conscious  life  (see  p.  259). 

Students  of  animal  behavior  are  in  the  habit  of  investigating 
the  ability  of  animals  to  make  simple  associations  by  training 
them  to  perform  particular  acts  under  conditions  such  that  the 
normal  stimulus  to  the  act  is  always  accompanied  by  a  second 
stimulus  of  a  different  type.  After  many  repetitions  the  re- 
sponse may  be  obtained  by  presenting  the  second  or  collateral 
stimulus  without  the  first.  For  the  nervous  mechanism  of 
"associative  memory"  of  this  sort  see  p.  64.  Pawlow  has 
found  that  variations  in  the  amount  of  saliva  secreted  form  an 
especially  good  index  of  associations  of  this  type,  and  he  has  used 
this  method  extensively  in  analyzing  complex  reactions,  or  con- 
ditional reflexes,  as  he  calls  them.  See  the  summary  of  his 
researches  in  the  paper  by  Morgulis  cited  in  the  appended  bib- 
liography. 

Tactile  sensibility  is  entirely  absent  throughout  the  entire 
alimentary  canal  from  the  esophagus  to  the  rectum,  and  the 
same  holds  true  for  most  of  the  other  deep-seated  viscera  of  the 
body.  Even  the  substance  of  the  brain  is  insensitive  to  any 
kind  of  mechanical  irritation.  Sensibility  to  changes  in  tem- 
perature is  feebly  developed  or  absent  in  most  of  the  viscera,  the 
esophagus  and  anal  canal  being  very  sensitive  to  heat  and  cold, 
while  the  stomach  and  colon  are  feebly  sensitive  to  these  stimuli. 
The  entire  alimentary  canal  is  insensitive  to  hydrochloric  and 
organic  acids  in  concentrations  far  in  excess  of  what  ordinarily  oc- 
curs in  either  normal  or  pathological  conditions.  The  contact  of 
alcohol  with  all  parts  of  the  mucous  membrane  of  the  alimentary 
canal  gives  rise  to  a  sensation  of  warmth.  This  sensation  is 
different  in  character  from  that  caused  by  hot  fluids  and  is  prob- 
ably excited  through  the  sympathetic  nerves,  while  the  sensa- 
tion of  warmth  felt  in  consequence  of  the  passage  of  hot  fluid 
through  the  esophagus  is  excited  through  the  vagus. 

The  demonstrated  absence  of  tactile  sensibility  throughout 
the  mucous  membrane  of  the  stomach  and  intestine  is  considered 
by  Hertz  to  indicate  that  the  sensations  of  fulness  arising  from 
the  distention  of  different  parts  of  the  alimentary  canal  are  due 
to  the  stretching  of  the  muscular  coat,  and  that,  therefore,  these 
are  to  be  regarded  as-  varieties  of  the  muscle  sense.     The  same 


THE    VISCERAL    AND    GUSTATORY    APPARATUS  243 

may  also  be  true  of  the  bladder;  The  free  nerve-endings  (see 
Fig.  33,  p.  90)  known  to  be  present  in  these  mucous  membranes, 
particularly  in  the  bladder,  may,  however,  share  in  exciting  these 
sensations,  for  these  membranes  may  well  be  sensitive  to  stretch- 
ing, even  though  quite  insensitive  to  simple  pressure.  The  only 
immediate  cause  of  true  visceral  pain  is  tension,  and  it  is  stated 
by  Hertz  that,  so  far  as  the  alimentary  canal  is  concerned,  this 
tension  is  exerted  on  the  muscular  coat,  not  on  the  mucous 
lining.     See  the  further  discussion  of  visceral  pain,  p.  250. 

The  vomiting  reflex  may  be  caused  by  excitations  of  sensory 
termini  of  the  vagus  nerve  in  the  stomach,  which  are  transmitted 
to  the  nucleus  of  the  fasciculus  solitarius  in  the  medulla  oblon- 
gata, whence  the  nervous  impulses  are  distributed  as  shown  in 
Fig.  113  to  the  appropriate  motor  centers. 

The  Gustatory  Apparatus. — Taste,  hke  smell,  is  a  chemical 
sense  (see  pp.  75,  91,  218).  Physiologically,  it  is  classed  by 
Sherrington  as  an  interoceptive  or  visceral  sense,  and  its  primary 
cerebral  center  is  intimately  joined  to  the  general  visceral 
sensory  center  in  the  nucleus  of  the  fasciculus  solitarius.  Unlike 
the  general  visceral  sensory  system,  however,  its  peripheral 
fibers  have  no  connection  with  the  sympathetic  nervous  system 
and  the  reactions  may  be  vividly  conscious.  The  end-organs, 
or  taste-buds  (Fig.  35,  p.  91),  are  present  in  the  mucous  mem- 
brane of  the  tongue,  soft  palate,  and  pharynx  and  are  innervated 
by  the  VII  and  IX  cranial  nerves;  there  are  a  few  taste-buds  also 
on  the  larynx  and  epiglottis  which  are  probably  supplied  by  the 
vagus  (J.  G.  Wilson).  All  of  these  peripheral  gustatory  fibers, 
upon  entering  the  medulla  oblongata,  terminate  in  the  nucleus 
of  the  fasciculus  solitarius  (Figs.  71,  72,  73,  114)  along  with 
those  of  general  visceral  sensibility,  those  of  the  gustatory  sys- 
tem probably  ending  farther  forward  (toward  the  mouth)  in  this 
nucleus  than  those  of  the  general  visceral  systems. 

There  has  been  considerable  controversy  as  to  the  exact  course 
taken  by  the  peripheral  nerves  of  taste  on  their  way  to  the  brain, 
many  clinical  neurologists  believing  that  all  of  these  fibers  enter 
the  medulla  oblongata  through  the  root  of  the  V  cranial  nerve. 
It  has  now  been  clearly  shown  by  the  studies  of  Gushing  and 
others  that  the  V  nerve  takes  no  part  in  the  innervation  of 
taste-buds.     Figure   115   shows   in  continuous  lines  the   true 


244 


INTRODUCTION   TO   NEUROLOGY 


V  motor 


V  sensory 
Nuc.  sensory  V 


VIII 

IX  motor 

X  motor 

XI  pars  bulbaris 

XI  pars  spinalis 

Nuc.  dorsalis  X' 

NuG.  ambiguus 


cmerea 
Fasciculus  solitarius 
Nuc.  commissuralis  Cajal 

Nuc.  spinalis  V 


Fig.  114. — Diagram  of  the  visceral  afferent  and  efferent  connections  in 
the  medulla  oblongata,  based  on  Fig.  71;  compare  also  Figs.  77  and  86. 
The  afferent  roots  and  centers  are  indicated  on  the  right  side;  the  efferent, 
on  the  left.  Visceral  sensory  fibers  enter  by  the  VII  nerve  (pars  intermedia 
of  Wrisberg,  VII  pars,  int.)  and  by  the  IX  and  X  nerves.  These  root-fibers 
include  both  general  visceral  sensory  and  gustatory  fibers,  all  of  which  enter 
the  fasciculus  sohtarius.  (Fibers  of  the  IX  and  X  nerves  also  enter  the 
spinal  V  tract;  but  since  these  are  somatic  sensory  fibers  from  the  auricular 
branch  they  are  not  included  in  the  diagram.  For  further  details  on  the 
composition  of  these  cranial  nerves  see  the  table  on  pp.  146,  147.) 

On  the  left  side  of  the  figure  the  general  visceral  efferent  nuclei  are  indi- 
cated by  small  dots  and  the  special  visceral  nuclei  by  large  dots.  The 
latter  comprise  the  motor  V  nucleus  for  the  jaw  muscles,  the  motor  VII 
nucleus  for  the  muscles  related  to  the  hyoid  bone  and  the  general  facial 
musculature,  and  the  nucleus  ambiguus  supplying  striated  muscles  of  the 
pharynx  and  larynx  by  way  of  the  IX  and  X  nerves.  Three  general  visceral 
efferent  nuclei  are  indicated — the  dorsal  motor  nucleus  of  the  vagus  under 
the  ala  cinerea  and  the  superior  and  inferior  salivatory  nuclei.  The  superior 
nucleus  (nuc.  sal.  sup.)  supplies  the  sublingual  and  submaxillary  salivary 
glands  by  way  of  the  VII  nerve  (pars  intermedia  of  Wrisberg),  and  the  in- 
ferior nucleus  {nuc.  sal.  inf.)  supplies  the  parotid  salivary  gland  by  way  of 
the  IX  nerve.  All  of  the  general  visceral  efferent  fibers  are  preganglionic 
sympathetic  fibers  (see  p.  229)  which  end  in  sympathetic  ganglia,  whence 
postganglionic  fibers  carry  the  nervous  impulses  onward  to  their  respective 
destinations. 


THE   VISCERAL    AND    GUSTATORY   APPARATUS 


245 


courses  of  the  nerve-fibers  from  the  taste-buds  of  the  tongue 
through  the  VII  and  IX  nerves,  and  in  broken  and  dotted  lines 
some  of  the  other  courses  which  have  been  suggested. 

In  fishes  the  gustatory  system  is  much  more  extensively  developed  than 
in  mammals,  especially  the  vagal  part  which  supphes  taste-buds  in  the  gill 
region.  In  some  species  of  fishes,  moreover,  taste-buds  appear  in  great 
numbers  in  the  outer  skin,  and  these  are  in  all  cases  innervated  from  the  VII 


Fig.  115. — Diagram  showing  some  of  the  various  courses  which  have  been 
advocated  for  the  taste  fibers  in  man.  The  courses  advocated  in  this 
work  are  shown  by  heavy  black  lines;  other  suggested  coiirses  are  indicated 
by  broken  or  dotted  lines:  fac.  rt.,  motor  facial  root;  G.G.,  Gasserian  gang- 
hon;  G.g.,  geniculate  ganglion;  G.  otic,  otic  ganghon;  G.  petr.,  ganghon 
petrosum;  G.  sp.,  sphenopalatine  ganglion ;  ^.s.  p.,  great  superficial  petrosal 
nerve;  N.  fac,  facial  trunk;  N.  Jac,  Jacobson's  or  the  tympanic  nerve; 
N.  vid.,  vidian  nerve;  Rami  anast.,  anastomotic  rami  between  the  geniculate 
ganglion  and  tympanic  plexus  and  the  small  and  great  superficial  petrosal 
nerves  respectively;  s.  s.  p.,  small  superficial  petrosal  nerve;  Tymp.,  tym- 
panum.    (After  Gushing.) 


cranial  nerve.  In  the  common  horned-pouts  or  catfishes  and  in  the  carps 
and  suckers  these  cutaneous  taste-buds  are  distributed  over  practically  the 
entire  body  surface,  and  especially  on  the  barblets.  The  distribution  of 
these  cutaneous  gustatory  branches  of  the  facial  nerve  in  the  common  bull- 
pout,  Ameiurus,  is  shown  in  Fig.  116.  These  sense-organs  and  their  nerves 
are  entirely  independent  of  those  of  the  lateral  line  sensory  system  and  of  the 
ordinary  tactile  system,  though  the  gustatory  and  the  tactile  systems  have 
been  shown  experimentally  to  cooperate  in  the  selection  of  food.  The 
primary  terminal  nuclei  of  these  gustatory  nerves  make  up  by  far  the  larger 


246 


INTRODUCTION   TO    NEUROLOGY 


part  of  the  visceral  area  (Fig.  43,  p.  Ill)  of  fish  brains,  and  in  some  species 
these  centers  are  enormously  enlarged,  as  in  the  carp  (Fig.  136  (2),  p.  303). 

The  primary  sensory  center  for  the  nerves  of  taste  in  the 
nucleus  of  the  fasciculus  solitarius  is  very  intimately  connected 
with  all  of  the  motor  centers  of  the  medulla  oblongata  for  the 
reactions  of  mastication  and  sv/allowing,  and  also  with  the  motor 
centers  of  the  spinal  cord.  The  ascending  path  from  the  prim- 
ary gustatory  nucleus  to  the  thalamus  and  cerebral  cortex  is 
wholly  unknown  in  the  human  body.     A  gustatory  center  is 


Fig.  116. — The  cutaneous  gustatory  branches  arising  from  the  geniculate 
ganglion  of  the  facial  nerve  of  the  catfish  (Ameiurus  melas),  projected  upon 
the  right  side  of  the  body.  Spinal  cord  and  brain  stippled.  The  geniculate 
ganglion,  its  roots  and  cutaneous  branches  are  drawn  in  black;  the  branches 
of  this  nerve  distributed  to  the  mucous  lining  of  the  mouth  cavity  are 
omitted.  Taste-buds  are  found  in  all  parts  of  the  outer  skin  to  which  these 
branches  are  distributed. 


believed  to  exist  in  the  cortex  of  the  gyrus  hippocampi  near  the 
anterior  end  of  the  temporal  lobe.  In  fishes,  where  this  ascend- 
ing gustatory  path  is  much  larger,  it  has  been  followed  to  the 
roof  of  the  midbrain  and,  after  a  synapse  here,  to  the  region  of 
the  hypothalamus. 

Visceral  Efferent  Centers. — The  arrangement  of  the  visceral 
efferent  nuclei  and  nerve-roots  of  the  medulla  oblongata  is  shown 
in  Fig.  114.  There  is  also  a  general  visceral  efferent  component 
of  the  III  cranial  nerve  (Fig.  71,  p.  154,  nuc.  III.  E-W.),  whose 
fibers  pass  out  through  this  nerve  to  the  ciliary  ganglion  in  the 
orbit,  which  in  turn  connects  with  the  intrinsic  muscles  of  the 


THE    VISCERAL    AND    GUSTATORY    APPARATUS  247 

eyeball  in  the  ciliary  process  and  iris.  These  fibers  are  involved 
in  the  movements  of  accommodation  of  the  eye  for  distance  and 
in  the  regulation  of  the  diameter  of  the  pupil.  The  nucleus  of 
the  fasciculus  solitarius  is  connected  through  the  reticular  forma- 
tion with  all  of  the  motor  centers  of  the  medulla  oblongata  for 
the  reactions  of  mastication  and  swallowing  and  for  many  other 
movements;  from  this  nucleus  there  is  a  descending  tract  to  the 
motor  centers  of  the  spinal  cord,  the  tractus  solitario-spinalis 
(Figs.  112  and  113).  There  is  also  a  connection  with  the  supe- 
rior and  inferior  salivatory  nuclei  of  the  VII  and  IX  nerves. 
The  excitation  of  the  gustatory  fibers  of  these  nerves  by  the 
presence  of  food  in  the  mouth  is  carried  to  the  nucleus  of  the 
fasciculus  solitarius  and  thence  through  the  reticular  formation 
to  the  salivatory  nuclei,  from  which  the  flow  of  saliva  is  excited. 
There  are  other  connections  with  the  motor  centers  of  the  spinal 
cord  through  the  descending  fibers  of  the  fasciculus  solitarius, 
some  of  these  fibers  crossing  to  the  opposite  side  in  the  vicinity 
of  the  commissural  nucleus  of  Cajal  (Fig.  114). 

Summary. — The  cerebro-spinal  visceral  systems  fall  into  a 
general  group  related  peripherally  to  the  sympathetic  nerves  and 
a  special  group  independent  of  the  sympathetic.  The  second 
group  includes  the  apparatus  for  taste  and  probably  for  smell. 
The  central  innervation  of  the  viscera  is  partly  from  the  spinal 
and  midbrain  regions,  but  chiefly  from  the  visceral  area  of  the 
medulla  oblongata.  The  heart  and  blood-vessels  have  a  double 
innervation  derived  from  both  the  spinal  and  the  bulbar  visceral 
centers,  and  the  nervous  control  of  the  organs  of  circulation  is 
very  complex.  Respiration  in  lower  vertebrates  is  effected  by 
strictly  visceral  structures  and  is  controlled  from  the  visceral 
area  of  the  medulla  oblongata.  In  mammals  the  muscles  of 
ordinary  respiration  are  all  of  the  somatic  type,  but  the  centers 
of  control  are  retained  in  the  visceral  area  of  the  oblongata.  The 
sensations  related  to  the  digestive  tract  are  served  chiefly 
(though  not  exclusively)  by  the  vagus.  There  are  special  sali- 
vatory nuclei  related  to  the  VII  and  IX  cranial  nerves.  The 
nerves  of  taste  are  the  VII,  IX,  and  to  a  very  limited  extent  (in 
man)  the  X  pairs  of  cranial  nerves.  The  primary  cerebral  gus- 
tatory center  is  in  the  upper  part  of  the  nucleus  of  the  fasciculus 
solitarius,  but  the  cortical  path  is  unknown. 


248  INTRODUCTION   TO   NEUROLOGY 

Literature 

Any  of  the  larger  text-books  of  physiology  will  give  further  details  of  the 
visceral  reactions.  For  a  very  brief  and  simple  account  of  the  circulatory 
apparatus  see  the  book  by  Stiles  (pp.  118-125)  cited  below.  The  experi- 
ments of  Molhant  have  given  us  the  most  detailed  information  regarding 
the  visceral  functions  of  the  vagus  and  their  centers  in  the  medulla  oblon- 
gata. 

Cannon,  W.  B.  1898.  The  Movements  of  the  Stomach  Studied  by 
Means  of  the  Rontgen  Rays,  Amer.  Jour.  Physiol.,  vol.  i,  pp.  359-382. 

— .  1902.  The  Movements  of  the  Intestines  Studied  by  Means  of  the 
Rontgen  Rays,  Amer.  Jour.  Physiol.,  vol.  vi,  p.  251. 

— .  1912.  Peristalsis,  Segmentation,  and  the  Myenteric  Reflex,  Amer. 
Jour.  Physiol.,  vol.  xxx,  pp.  114-128. 

Cannon,  W.  B.,  and  Washburn,  A.  L.  1912.  An  Explanation  of  Hunger, 
Amer.  Jour.  Physiol.,  vol.  xxix,  pp.  441-450. 

Carlson,  A.  J.  1912-1915.  Contributions  to  the  Physiology  of  the 
Stomach,  Amer.  Jour.  Physiol.,  vols,  xxxi-xxxv. 

CusHiNG,  H.  1903.  The  Taste  Fibers  and  Their  Independence  of  the 
N.  Trigeminus,  Johns  Hopkins  Hospital  Bulletin,  vol.  xiv,  pp.  71-78. 

Herrick,  C.  Judson.  1903.  The  Organ  and  Sense  of  Taste  in  Fishes, 
Bui.  U.  S.  Fish  Commission  for  1902,  pp.  237-272. 

— .  1905.  The  Central  Gustatory  Paths  in  the  Brains  of  Bony  Fishes, 
Jour.  Comp.  Neurol.,  vol.  xv,  pp.  375-456. 

— .  1908.  On  the  Commissura  Infima  and  Its  Nuclei  in  the  Brains  of 
Fishes,  Jour.  Comp.  Neurol.,  vol.  xviii,  pp.  409-431. 

Hertz,  A.  F.  1911.  The  Sensibility  of  the  Alimentary  Canal,  London, 
Oxford  University  Press. 

Kappers,  C.  U.  a.  1914.  Der  Geschmack,  perifer  und  central,  zugleich 
eine  Skizze  der  phylogenetischen  Veranderungen  in  der  sensibelen  VII,  IX, 
und  5^  Wurzeln,  Psychiat.  en  Neurol.,  Bladen, , pp.  1-57. 

Molhant,  M.  1910-1913.  Le  nerf  vague:  Etude  anatomique  et  experi- 
mentale,  Le  Nevraxe,  vols,  xiii-xv. 

Morgulis,  S.  1914.  Pawlow's  Theory  of  the  Function  of  the  Central 
Nervous  System  and  a  Digest  of  Some  of  the  More  Recent  Contributions 
to  this  Subject  from  Pawlow's  Laboratory,  Jour.  Animal  Behavior,  vol.  iv, 
pp.  362-379. 

Pawlow,  I.  1913.  The  Investigation  of  the  Higher  Nervous  Func- 
tions, Brit.  Med.  Jour.,  vol.  ii  for  1913,  pp.  973-978. 

Sheldon,  R.  E.  1909.  The  Phylogeny  of  the  Facial  Nerve  and  Chorda 
Tympani,  Anat.  Record,  vol.  iii,  pp.  593-617. 

— .  1909.  The  Reactions  of  the  Dogfish  to  Chemical  Stimuli,  Jour. 
Comp.  Neurol.,  vol.  xix,  pp.  273-311. 

Stiles,  P.  G.  1915.  The  Nervous  System  and  Its  Conservation,  Phila- 
delphia. 

Wilson,  J.  G.  1905.  The  Structure  and  Function  of  the  Taste-buds  of 
the  Larynx,  Brain,  vol.  xxviii,  pp.  339-351. 


CHAPTER  XVIII 

PAIN    AND    PLEASURE 

Few  problems  in  neurology  are  more  difficult  and  involved 
than  those  centering  about  the  nerves  of  painful  sensibility. 
This  question  is  intimately  related  with  the  disagreeable  and 
pleasurable  feelings  and  with  the  affective  and  emotional  life  as  a 
whole.  Nearly  all  sensations,  whether  of  the  somatic  or  visceral 
series,  appear  to  have  an  agreeable  or  disagreeable  quality 
(quale) .  There  is  difference  of  opinion  as  to  whether  any  sensa- 
tion is  wholly  indifferent  in  this  respect.  There  are,  however, 
two  factors  in  this  situation  which  have  not  always  been  dis- 
tinguished and  whose  introspective  analysis  is  very  difficult. 
In  the  first  place,  many  sensations  are  as  such  painful  or  pleasur- 
able, and  in  the  second  place  the  related  apperceptions,  ideas, 
etc.,  may  have  an  agreeable  or  disagreeable  feeling  tone.  The 
intimate  relation  of  these  two  factors  in  consciousness  probably 
grows  out  of  a  similarity  in  the  type  of  physiological  process 
involved  in  their  neurological  mechanisms,  and  this,  in  turn, 
may  rest  on  the  fact  that  the  two  mechanisms  in  question  have 
had  a  common  evolutionary  origin. 

The  stimulation  of  some  of  the  sense  organs  results  in  the  so- 
called  sensation  of  pain  with  no  other  quality  recognizable; 
this  is  true  of  the  cornea,  of  the  tooth  pulps,  of  the  tympanic 
membrane,  and  of  the  "pain  spots"  of  the  outer  skin.  This  fact 
would  suggest  that  there  is  a  special  system  of  neurons  (or  at 
least  of  receptors,  see  p.  85)  for  pain  as  for  the  other  senses. 
But,  on  the  other  hand,  the  supernormal  stimulation  of  most 
other  sense  organs  may  result  in  a  very  similar  type  of  pain, 
though  in  this  case  the  painful  quality  is  accompanied  by  the 
normal  sensory  quality  of  the  organ  in  question  unless  the  stimu- 
lation is  excessively  strong.  From  this  it  would  appear  that 
most  sensory  nerves  may  upon  occasion  function  as  pain  nerves. 
In  other  cases  normal  stimulation  of  a  sense  organ  may  result  in 

249 


250  INTRODUCTION  TO  NEUROLOGY 

a  sensation  of  the  quality  typical  for  the  organ  in  question,  to 
which  there  is  added  an  agreeable  or  disagreeable  quality  which 
may  be  very  pronounced,  the  disagreeable  quality  not  being 
painful  in  the  ordinaiy  sense  of  that  term.  This  mixed  quality 
of  normal  sensations  is  illustrated  by  certain  odors  and  savors, 
and  on  the  agreeable  side  by  certain  sensations  of  tickle  and 
warmth.  Finally,  some  ideational  processes  have  an  agreeable 
or  disagreeable  quality,  and  these,  in  turn,  are  very  intimately 
related  with  the  emotions  and  with  esthetic  and  appreciative 
functions  of  the  most  complex  psychic  sort,  as  well  as  with  ques- 
tions of  habitual  emotional  attitude  and  temperament. 

The  superficial  parts  of  the  body  which  are  more  directly  ex- 
posed to  traumatic  injury  are,  in  general,  more  sensitive  to  pain 
than  are  the  deeper  parts,  and  painful  stimuli  here  can  be  more 
accurately  localized.  In  some  parts,  like  the  conjunctiva  of  the 
eyeball,  where  very  slight  irritation  may  seriously  interfere 
with  the  function,  very  gentle  stimulation  gives  rise  to  acute 
pain,  and  no  other  sensory  quality  may  be  present. 

Surgeons  find  that  the  brain  membranes  are  sensitive  to 
mechanical  injury,  especially  to  stretching  or  pulling.  The  brain 
substance  itself,  however,  is  quite  insensitive  to  pain  from  either 
mechanical  or  chemical  stimulation.  The  deeper  viscera  of  the 
thorax  and  abdomen  are  insensitive  to  pinching,  cutting  with  a 
sharp  instrument,  or  other  mechanical,  chemical,  or  thermal 
stimuH,  though  they  are  sensitive  to  pains  arising  from  internal 
disorders,  as  in  cohc  (p.  243).  The  visceral  portions  of  the 
pleural  and  peritoneal  membranes  are  insensitive  to  pain,  but 
their  parietal  portions,  forming  the  innermost  layer  of  the  body 
wall,  are  sensitive,  and  these  pains  can  be  accurately  localized 
(Capps). 

From  these  considerations  it  appears  that  pain  is  an  adaptive 
function  which  is  present  only  where  it  is  of  value  to  give  warn- 
ing of  noxious  influences  hable  to  injure  the  body  unless  re- 
moved. (See  the  excellent  discussion  by  Sherrington  in 
Schafer's  Physiology,  vol.  ii,  pp.  965-1001.) 

Pains  of  this  sort  are  physiologically  similar  to  other  extero- 
ceptive sensations,  that  is,  they  have  a  definite  localization  and 
are  externally  projected  like  other  somatic  sensations.  But 
other  pains  and  discomforts  (especially  those  related  to  the 


PAIN    AND    PLEASURE  251 

visceral  functions)  and  all  pleasurable  feelings  are  devoid  of  this 
external  projicience  and  are  experienced  merely  as  a  non-local- 
ized awareness  of  malaise  or  well-being  (see  p.  259).  They  are 
also  more  variable  in  relation  to  habit,  mental  attitude,  fatigue, 
and  general  health.  This  latter  group  of  affective  processes  is  so 
different  from  the  ordinary  sensations  as  to  make  it  desirable  to 
consider  them  separately,  an'd,  as  will  appear  beyond,  they  prob- 
ably involve  a  quite  different  series  of  nervous  processes. 

There  has  been  much  controversy  regarding  the  pathway 
taken  by  painful  impulses  through  the  spinal  cord  and  brain 
stem,  and  it  is  probable  that  this  pathway  is  very  complex. 
All  painful  impulses  carried  by  the  spinal  nerves,  no  matter 
what  the  peripheral  source,  are  discharged  immediately  upon 
entering  the  spinal  cord  into  its  gray  matter,  and  after  a  synapse 
here  the  nerve-fibers  of  the  second  order  seem  to  take  several 
courses.  The  most  recent  experiments  (Karplus  and  Kreidl, 
1914)  go  to  show  that  the  ascending  impulses  of  painful  sensi- 
bility in  the  spinal  cord  of  cats  follow  a  chain  of  short  neurons, 
some  of  whose  axons  immediately  cross  to  the  opposite  side  of 
the  cord  and  some  ascend  on  the  same  side.  These  short  fibers 
belong  to  the  fasciculus  proprius  system  (p.  127),  and  the  nervous 
impulse  is  at  frequent  intervals  returned  to  the  gray  matter  to 
pass  from  one  neuron  to  another,  and  it  may  cross  the  midplane 
repeatedly.  This  diffuse  method  of  conduction  appears  to  be 
the  primitive  arrangement.  In  the  human  spinal  cord  it  is 
probably  present  to  a  limited  extent,  but  has  been  largely  sup- 
planted by  a  more  direct  pathway  in  the  spinal  lemniscus,  whose 
precise  localization  has  been  determined  by  the  clinical  studies  of 
Henry  Head  and  others  (pp.  139, 173).  This  direct  path  for  fibers 
of  painful  sensibility  includes  axons  of  neurons  of  the  dorsal  gray 
column,  which  immediately  cross  to  the  opposite  side  of  the  cord 
and  ascend  directly  to  the  thalamus.  Injury  to  this  path  in  the 
human  body  may  cause  complete  insensitivity  to  both  superficial 
and  deep  pain  on  the  opposite  side  of  the  body  below  the  site 
of  the  injury,  without  loss  of  general  tactile  sensibility.  The 
two  methods  of  transmission  of  impulses  of  painful  sensibility 
are  shown  diagrammatically  in  Fig.  117. 

It  may  be  assumed  that  pain  and  an  avoiding  reaction  and  pleasure  and  a 
seeking  reaction  have  come  to  be  instinctively  associated  by  natural  selec- 


252 


INTRODUCTION   TO    NEUROLOGY 


tion  or  other  biological  agencies  because  this  is  an  adaptation  useful  to  the 
organism.  No  separate  neurons  would  be  required  for  the  transmission  and 
analysis  of  painful  stimuli  in  their  simpler  forms.  A  peripheral  neuron,  say, 
of  the  pressure  sense,  if  excited  by  the  optimum  stimulus  wiU  transmit  the 
appropriate  nervous  impulse  to  the  tactile  centers  of  the  thalamus  and  cere- 
bral cortex.  But  the  peripheral  sensory  neurons  branch  widely  within  the 
spinal  cord  and  there  effect  very  diverse  types  of  connection  (see  Fig.  61,  p. 
134) ;  and  supernormal  or  maximal  stimulation  of  the  end-organ  may  excite 
so  strong  a  nervous  discharge  as  to  overflow  the  tactile  pathway  in  the  spinal 


To  the  thalamus 


Fasciculus  proprius 
Spinal  lemniscus 


Spinal  nerve 


Fig.  117. — Diagram  of  the  pathways  of  painful  sensibility  in  the  spinal 
cord.  The  spinal  lemniscus  is  the  dominant  path  in  the  human  body,  and 
the  fasciculus  proprius  is  the  dominant  path  in  other  mammals. 


cord  by  overcoming  the  synaptic  resistance  of  certain  other  collateral  path- 
ways with  a  higher  threshold  than  those  of  the  tactile  path,  thus  exciting  to 
function  the  pathway  for  painful  sensibility  with  its  own  central  connection 
in  the  thalamus  (Fig.  118,  A). 

In  the  course  of  the  further  differentiation  of  the  cutaneous  receptors, 
the  peripheral  fiber  of  the  sensory  neuron  may  branch  and  effect  connection 
with  two  types  of  sense  organs,  one  organ  (a  tactile  spot)  with  a  low  thresh- 
old for  pressure  stimuh  whose  nervous  impulses  are  so  attuned  as  to  dis- 


PAIN    AND    PLEASURE 


253 


charge  centrally  at  the  first  synapse  into  the  tactile  tract,  and  another  organ 
differently  constructed  (a  pain  spot)  which  generates  nervous  impulses  so 
attuned  as  to  discharge  centrally  into  the  pain  tract  (Fig.  118,  Bj.  In  a 
still  more  highlj-  elaborated  system  two  separate  peripheral  neurons  may  be 
present  to  serve  these  functions,  which  are  distinct  throughout  (Fig.  118,  C). 
All  three  of  these  methods  of  pain  transmission  and  analysis  may  be  present 
in  the  spinal  nerves;  but  by  whatever  pathway  the  pain  impulses  reach  the 
spinal  cord,  in  the  human  body  those  which  are  destined  to  excite  conscious- 
ness of  pain  as  a  localizable  sensation  are  immediately  filtered  off  from  the 
other  .sensory  quaUties  with  which  they  may  be  associated  and  assembled  in 
a  pathway  of  their  own,  which  remains  distinct  from  this  time  forth.  With- 
in the  spinal  cord  and  brain  stem  these  pain  impulses,  especially  those  result- 
ing from  supernormal  stimulation,  also  effect  short  reflex  connections  with 
the  adjacent  motor  centers  for  quick  avoiding  reflexes,  and  these  may  not 
be  associated  with  the  spinal  lemniscus,  but  with  the  more  diffuse  pain  path 
in  the  fasciculus  proprius. 


pain  path 
tactile  path 
sKin 


spinal  cord 


pain  path 
tactile  path 


tactile 
spot 


spinal  cord 


'tactile 
spot 


spinal  cord 


Fig.  118. — Three  diagrams  to  illustrate  various  ways  in  which  the 
nerves  of  painful  sensibility  may  be  associated  with  those  of  other  sensory 
functions. 


The  terminus  of  the  ascending  pain  tract  is  related  within  the 
thalamus  very  differently  from  those  of  the  pathways  for  tactile 
and  thermal  sensitivity.  The  latter  impulses  are  in  part  trans- 
mitted to  the  motor  centers  of  the  thalamus  for  intrinsic  thalamic 
reflexes,  but  chiefly  pass  forward  after  a  synapse  in  the  thalamus 
through  the  internal  capsule  to  the  somesthetic  areas  of  the 
cerebral  cortex.  Head  is  of  the  opinion  that  the  painful  im- 
pulses do  not  reach  the  cortex  at  all  in  their  simple  elementary 
form,  but  that  the  painful  sensations  are  essentially  thalamic. 

Le.sions  of  the  lateral  and  ventral  nuclei  of  the  thalamus  in- 
volving the  termini  of  the  lemniscus,  but  leaving  the  geniculate 
bodies  and  pulvinar  and  the  medial  and  anterior  nuclei  intact, 
result  in  the  more  or  less  complete  loss  of  superficial  sensation  of 
the  opposite  side  of  the  body,  with  still  more  profound  disturb- 


254  INTRODUCTION  TO  NEUROLOGY 

ance  of  deep  sensibility  and  the  postural  sensations,  together 
with  an  exaggeration  of  painful  sensibility.  The  modifications 
of  pain  and  affective  sensibility  are  regarded  by  Head  and 
Holmes  as  the  most  constant  and  characteristic  features  of  le- 
sions of  the  lateral  zone  of  the  thalamus.  Acute,  persistent, 
paroxysmal  pains  are  always  present,  often  intolerable  and 
yielding  to  no  analgesic  treatment.  There  is  also  a  tendency  to 
react  excessively  to  unpleasant  stimuli.  This  is  not  necessarily 
associated  with  a  lowering  of  the  threshold  of  stimulation. 
Deep  pressure  is  especially  important  here.  The  pain  does  not 
develop  gradually  out  of  the  general  sensation,  but  appears 
explosively.  This  pain  has  some  factor  to  which  the  normal  half 
of  the  body  is  not  particularly  susceptible.  Thermal,  visceral, 
and  other  sense  qualities  are  similarly  affected.  Tickling  is  very 
unpleasant  on  the  affected  side.  The  pleasurable  aspect  of 
moderate  heat  is  accentuated  on  the  affected  side,  yet  the 
threshold  for  heat  is  never  lowered.  Not  only  does  the  side  of 
the  body  involved  react  more  vigorously  to  an  affective  element 
of  a  stimulus,  but  an  overreaction  can  also  be  evoked  by  purely 
mental  states.  The  manifestations  of  this  increased  suscepti- 
bility to  states  of  pleasure  and  pain  are  strictly  unilateral. 
Associated  with  this  overreaction  to  painful  stimuli  some  loss 
of  general  sensation  will  always  be  manifest  on  the  affected  side 
of  the  body. 

Pure  cortical  lesions  cause  no  change  in  the  threshold  to  pain, 
nor  is  there  the  exaggerated  affective  quality  characteristic  of 
thalamic  lesions.  Head  and  Holmes  assume  that  both  the 
thalamus  and  the  cortex  are  concerned  in  conscious  activity. 
They  say: 

"The  most  remarkable  feature  in  that  group  of  thalamic  cases  with 
which  we  have  dealt  in  this  work  is  not  the  loss  of  sensation,  but  an  excessive 
response  to  affective  stimuU.  This  positive  effect,  an  actual  overloading  of 
sensation  with  feeling  tone,  was  present  in  all  our  24  cases  of  this  class." 
This  effect  is  interpreted  as  due  to  the  release  of  the  inhibitory  or  regulatory 
influence  of  the  cortex  arising  from  the  destruction  of  the  ascending  and 
descending  fibers  between  the  thalamus  and  the  cortex,  thus  isolating  the 
thalamus  and  allowing  it  to  act  to  excess.  These  authors  add,  since  "the 
affective  states  can  be  increased  when  the  thalamus  is  freed  from  cortical 
control,  we  may  conclude  that  the  activity  of  the  essential  thalamic  center 
is  mainly  occupied  with  the  affective  side  of  sensation."  "This  conclusion  is 
strengthened  by  the  fact  that  stationary  cortical  lesions,  however  extensive, 


PAIN    AND    PLEASURE  255 

which  cause  no  convulsions  or  other  signs  of  irritation  and  shock,  produce 
no  effect  on  sensibility  to  pain.  Destruction  of  the  cortex  alone  does  not 
disturb  the  threshold  for  the  painful  or  uncomfortable  aspects  of  sensation."' 

Some  recent  experiments  bj^  Cannon  have  revealed  a  very 
intimate  relation  between  emotion  and  some  of  the  ductless 
glands.  The  suprarenal  (or  adrenal)  glands,  situated  above  the 
kidneys,  secrete  and  pour  into  the  blood  a  remarkable  substance 
known  as  adrenalin  or  epinephrin.  This  substance  exerts  upon 
structures  which  are  innervated  by  sj^mpathetic  nerves  the  same 
effects  as  are  produced  by  impulses  passing  along  those  nerves. 
The  glands  may  themselves  be  excited  to  activity  by  nervous 
impulses  passing  out  through  the  sympathetic  nerves.  Cannon 
has  shown  that  the  emotions  of  fear,  rage,  and  pain  excite  these 
glands  to  activity  and  cause  the  secretion  of  adrenalin.  The 
blood  of  a  caged  cat  which  has  been  tormented  by  the  barking  of 
a  dog  will  show  an  increased  percentage  of  adrenalin.  The 
addition  of  adrenalin  to  the  blood  has  the  further  effect  of  caus- 
ing liberation  of  sugar  from  the  liver  into  the  blood  to  such  an 
extent  that  sugar  may  appear  in  the  urine  (gty cosuria) ;  and  sugar 
is  known  to  be  the  most  available  form  in  which  energ}^  can  be 
quickly  supplied  to  tissues  which  have  been  exhausted  by  exer- 
cise. Adrenalin  will  in  this  and  other  ways  act  as  an  antidote  to 
muscular  fatigue.  It  also  renders  more  rapid  the  coagulation  of 
the  blood. 

If  a  muscle  is  fatigued,  the  threshold  of  irritability  rises.  It 
may  rise  as  much  as  600  per  cent.,  but  the  average  increase  is 
approximately  200  per  cent.  If  the  fatigued  muscle  is  allowed 
to  rest,  the  former  irritability  is  gradually  regained,  though  two 
hours  may  pass  before  the  recovery  is  complete.  If  a  small  dose 
of  adrenalin  is  administered  intravenously,  or  the  adrenal  glands 
are  stimulated  to  secrete.  Cannon  has  found  that  the  former  irri- 
tability of  the  fatigued  muscle  maj^  be  recovered  within  three 
minutes.  In  this  way  adrenal  secretion  maj^  largely  restore 
efficienc}^  after  fatigue. 

Fear  and  anger — as  well  as  worry  and  distress — are  attended 
by  cessation  of  the  contractions  of  the  stomach  and  intestines. 
These  mental  states  also  reduce  or  temporarily  abolish  the  secre- 
tion of  gastric  juice.  Adrenahn  injected  into  the  body  has  the 
same  effect.     Besides  checking  the  functions  of  the  alimentary 


256  INTRODUCTION  TO  NEUROLOGY 

canal,  adrenalin  drives  out  the  blood  which,  during  digestive 
activity,  floods  the  abdominal  viscera.  This  blood  flows  all  the 
more  rapidly  and  abundantly  through  the  heart,  the  lungs,  the 
central  nervous  system,  and  the  limbs. 

Cannon  epitomizes  the  account  from  which  the  above  has  been 
condensed  in  these  words:  "The  emotional  reactions  above 
described  may  each  be  interpreted,  therefore,  as  making  the 
organism  more  efficient  in  the  struggle  which  fear  or  rage  or 
pain  may  involve.  And  that  organism  which,  with  the  aid  of 
adrenal  secretion,  best  mobilizes  its  sugar,  lessens  its  muscular 
fatigue,  sends  its  blood  to  the  vitally  important  organs,  and 
provides  against  serious  hemorrhage,  will  stand  the  best  chance 
of  surviving  in  the  struggle  for  existence." 

The  preceding  account  includes  a  summary  of  some  of  the 
most  securely  established  facts  regarding  the  peripheral  and 
central  nervous  mechanisms  of  painful  impressions  and  the 
physiology  of  the  emotions,  together  with  a  theoretical  interpre- 
tation of  the  apparently  twofold  nature  of  pain  as  a  specific 
sensation  and  as  a  component  of  the  general  affective  state  of  the 
body  as  a  whole.  The  more  general  questions  concerning  the 
physiological  processes  related  with  pleasurable  and  unpleasant 
experience  and  the  affective  life  in  general  are  still  more  difficult 
of  analysis.  It  seems  probable  that  pain,  unpleasant  and 
pleasurable  feelings,  emotion,  and,  in  short,  the  entire  affective 
life  are  very  intimately  related  on  the  neurological  side. 

Many  physiological  theories  of  pleasure-pain  have  been  elaborated,  for 
the  most  part  on  very  slender  observational  grounds.  It  has  been  suggested 
that  the  flexor  movements  of  the  body  are  associated  with  pain,  the  extensor 
movements  with  pleasure;  that  constructive  metabolism  is  pleasurable, 
destructive  metabolism  disagreeable;  that  heightened  nervous  discharge  is 
pleasurable,  and  the  reverse  (some  form  of  inhibition  or  of  antagonistic 
contraction)  is  unpleasant.  Some  hold  that  pain  and  unpleasantness  or 
disagreeableness  are  different  in  degree  only,  not  in  kind.  Others  regard 
pain  as  a  true  sensation,  but  disagreeableness  and  pleasure  (affective  ex- 
perience) as  belonging  to  a  different  category  which  is  non-sensory.  In  the 
latter  case  the  affective  experience  may  be  neurologically  related  in  some 
way  with  the  various  sensations  (including  pain)  or  the  affective  experience 
and  sensations  may  be  independent  variables  with  separate  cerebral 
mechanisms.  None  of  these  hypotheses,  or  many  others  which  might  be 
mentioned,  are  competent  to  explain  satisfactorily  all  of  the  known  facts, 
though  strong  arguments  can  be  adduced  in  support  of  each  of  them. 

Our  own  view  is  that  pleasurable  and  unpleasant  experiences  are  not  true 
sensations,  that  in  the  history  of  the  psychogenesis  of  primitive  animals  a 


PAIN    AND    PLEASURE  257 

diffuse  unlocalized  affective  experience  of  well-being  or  malaise  probably 
antedated  anything  so  clearly  analyzed  as  a  sensation  with  specific  external 
reference,  and  that,  parallel  with  the  differentiation  of  true  sensations  of 
touch,  temperature,  and  so  on  in  consciousness,  pain  sensations  emerged  out 
of  the  diffuse  affective  experience  and  took  their  place  among  the  other  sense 
qualities.  An  essential  condition  for  the  appearance  in  consciousness  of  a 
definite  sensation  like  touch  or  vision  is  the  differentiation  in  the  nervous 
system  of  a  system  of  localized  tracts  and  centers  related  to  this  function, 
and  in  the  human  body  such  localized  tracts  and  centers  seem  to  be  present 
for  pain.  Pain,  therefore,  considered  psychologically  and  neurologically,  is 
a  sensation,  and  a  different  neurological  mechanism  for  unpleasantness  and 
pleasantness  must  be  sought.  To  this  problem  we  shall  next  turn  our 
attention. 

We  have  seen  above  that  it  is  possible  to  frame  a  neurological  hypothesis 
which  allows  a  given  peripheral  sensory  neuron  to  be  conceived  as  trans- 
mitting, say,  a  tactual  impression  from  the  skin  and  also  a  painful  im- 
pression from  the  same  or  a  different  end-organ.  Upon  reaching  the  spinal 
cord  the  nervous  impulses  of  the  tactual  series  may  pass  through  one  tj^^e  of 
spinal  synapse  to  the  spinal  lemniscus,  and  finally  reach  the  tactual  center 
of  the  cerebral  cortex,  and  the  nervous  impulses  of  the  painful  series  may  be 
drawn  off  through  a  second  system  of  synapses  for  transmission  through  a 
distinct  system  of  central  pathways.  Attention  has  also  been  called  to  the 
fact  that  the  specific  pain  nerves  and  central  paths  may  have  been  developed 
by  a  process  of  the  further  differentiation  of  separate  neurons  with  different 
peripheral  and  central  connections  for  these  two  functions.  But  what  of 
the  pleasurable  qualities  which  seem  similarly  to  be  associated  with  some 
sensory  impulses? 

The  simplest  view  seems  to  the  writer  to  be  that  the  normal  activity  of 
the  body  within  physiological  Umits  is  intrinsically  pleasurable,  so  far  as  it 
comes  into  consciousness  at  all.  There  is  a  simple  joy  of  living  for  its  own 
sake,  and  the  more  productive  the  Hfe  is,  within  well-defined  physiological 
limits  of  fatigue,  good  health,  and  diversified  types  of  reaction,  the  greater 
the  happiness.  The  expenditure  of  energy  within  these  physiological  limits 
is  pleasurable  per  se  except  in  so  far  as  various  psychological  factors  enter  to 
disturb  the  simple  natural  physiological  expression  of  bodily  activity.  Such 
disturbing  factors  are  anxiety,  want,  rebelhon  against  compulsory  service, 
and  unrelieved  routine.  The  expenditure  of  intelligently  directed  nervous 
energy  along  lines  of  fruitful  endeavor  is  probably  the  highest  tjiDe  of 
pleasure  known  to  mankind. 

But  it  should  be  borne  in  mind  that  the  normal  activities  of  the  body  are 
all  combined  into  adaptive  systems,  that  is,  they  are  directed  toward  the 
accomplishment  of  definite  ends  and  not  directed  at  random.  Even  in 
instinctive  activities  of  the  invariable  or  innate  type,  though  there  may  be  no 
consciousness  of  the  end  to  be  attained,  the  actions  are  not  satisfying  to  the 
animal  unless  they  follow  in  the  predetermined  adaptive  sequence  (p.  61). 
The  play  of  both  men  and  other  animals  is  likewise  always  correlated  around 
some  definite  physiological  motive.  And  it  is  even  more  conspicuously  true 
that  the  intelligently  directed  activities  are  unsatisf3ang  unless  they  attain, 
or  at  least  approximate  to,  some  particular  end.  Stated  in  other  words,  it  is 
not  the  activity  which  is  pleasurable,  so  much  as  the  accomplishment,  or,  in 
the  case  of  delayed  reactions,  the  hope  of  accomplishment. 

The  normal  discharge,  then,  of  definitely  elaborated  nervous  circuits 
resulting  in  free  unrestrained  activity  is  pleasurable,  in  so  far  as  the  reaction 

17 


258  INTRODUCTION  TO  NEUROLOGY 

comes  into  consciousness  at  all  (of  course,  a  large  proportion  of  such  reactions 
are  strictly  reflex  and  have  no  conscious  significance).  Conversely,  the 
impediment  to  such  discharge,  no  matter  what  the  occasion,  results  in  a 
stasis  in  the  nerve  centers,  the  summation  of  stimuh  and  the  development 
of  a  situation  of  unreUeved  nervous  tension  which  is  unpleasant  until  the 
tension  is  relieved  by  the  appropriate  adaptive  reaction.  Such  a  stasis 
may  be  brought  about  by  a  conflict  of  two  sensory  impulses  for  the  same 
final  common  path  (see  p.  59),  by  the  dilemma  occasioned  by  the  necessity 
for  discrimination  in  an  association  center  between  two  or  more  possible 
final  paths,  by  fatigue,  auto-intoxication,  or  other  physiological  states  which 
lower  the  efficiency  of  the  central  mechanism,  and  by  a  variety  of  other 
causes.  The  unrelieved  summation  of  stimuli  in  the  nerve  centers,  involving 
stasis,  tension,  and  interference  with  free  discharge  of  nervous  energy,  gives 
a  feehng  of  unpleasantness  which  in  turn  (in  the  higher  types  of  conscious 
reaction  at  least)  serves  as  a  stimulus  to  other  associated  nerve  centers  to 
participate  in  the  reaction  until  finally  the  appropriate  avenue  for  an 
adaptive  response  is  opened  and  the  situation  is  relieved.  With  the  release 
of  the  tension  and  free  discharge,  the  feeling  tone  changes  to  a  distinctly 
pleasurable  quality  (see  C.  L.  Herrick,  1910). 

The  fact  that  the  primitive  pain  path  in  the  spinal  cord  seems  to  follow 
a  rather  diffusely  arranged  system  of  fibers  in  the  fasciculus  proprius,  fre- 
quently interrupted  by  synapses  in  the  gray  matter  (Fig.  117)  with  corres- 
pondingly high  resistance  to  nervous  conduction,  is  perhaps  correlated  with 
this  general  and  diffuse  quality  of  unpleasantness. 

Now,  pain  as  a  distinct  and  localizable  sensation  has  not  been  involved 
in  the  situation  described  in  the  preceding  paragraphs.  Pain,  considered  as 
a  distinct  sensation,  was,  however,  born  out  of  this  situation  or  differentiated 
from  it.  Certain  sensational  elements  which  have  a  high  protective  value 
for  the  organism  are  naturally  most  often  involved  in  such  a  situation. 
These  are  warning  caUs,  and  usually  necessitate  an  interruption  of  the 
ordinary  business  of  life  which  may  be  in  process  at  the  time  the  danger 
threatens.  The  free  flow  of  ordinary  sensori-motor  activity  is  abruptly 
checked,  and  the  organism  suddenly  stops  and  makes  the  necessary  read- 
justment as  quickly  as  may  be.  In  the  interest  of  increasing  the  rapidity 
of  this  avoiding  reaction,  which,  of  course,  is  frequently  of  vital  importance, 
the  pathways  of  the  exteroceptive  pain  reactions  are  well  developed  and 
segregated  from  the  more  diffuse  and  poorly  organized  affective  apparatus 
which  we  have  just  been  considering.  Thus  arose  pain  nerves  (if  such  exist 
separately)  and  the  pain  tract  of  the  spinal  cord  (whose  anatomical  dis- 
tinctness seems  well  established),  and  also  perhaps  a  special  mechanism 
for  painful  reactions  in  the  thalamus.  Sherrington  has  given  a  graphic 
statement  of  the  probable  history  of  this  process  in  the  following  words 
(Schafer's  Physiology,  vol.  ii,  p.  974) : 

"The  facihty  of  path  of  these  motor  reflexes  colligated  to  pain  hints  at 
their  antiquity,  or  at  their  having  been  formed  by  some  neural  method  par- 
ticularly able  to,  as  it  were,  make  a  good  road.  Each  reaction  that  employs 
a  neural  path  seems  to  smooth  it  by  sheer  act  of  travel.  This  is  true  even 
of  slight  impulses — light  traffic — and  more  true  of  heavy.  Pain  reactions 
are  to  be  regarded  as  very  heavy  traffic.  Their  impressions  summate  with 
peculiar  ease,  take  correspondingly  long  periods  to  subside,  and,  to  judge 
by  their  inertia,  move  generally  masses  of  neural  material  relatively  great. 
Such  impressions  might  wear  a  road  with  quite  especial  speed.  Many 
spinal  reflexes  imply,  so  to  say,  well-worn  habits  based  on  ancient  pain 


PAIN    AND    PLEASURE  259 

reactions.  One  is  almost  emboldened  to  figiu-atively  imagine  them  as  con- 
nate memories  of  the  spinal  cord.  The  majority  of  them  seem  to  be  pro- 
tective reactions  that  in  organisms  of  high  neural  type  are  accompanied  by 
'pain.'" 

But  even  in  this  case  the  apparatus  for  pain  is  incapable  of  acting  as 
rapidly  as  are  those  of  some  other  sensations.  If  a  sensitive  corn  on  the  foot 
is  struck  a  sharp  blow,  one  will  often  feel  a  very  distinct  tactile  sensation  an 
appreciable  interval  before  the  painful  quality  is  perceived,  the  latter,  how- 
ever, soon  welling  up  into  consciousness  and  obscuring  the  tactile  quaUty 
entirely.  This  is  an  illustration  of  the  fact  that  even  the  highly  protective 
exteroceptive  painful  stimuli  pass  through  a  mechanism  of  slower  reaction 
time  than  the  primary  exteroceptive  sensations  with  which  they  may  be 
associated. 

We  cannot  here  enter  into  a  full  discussion  of  the  larger  questions  center- 
ing about  the  phj'siological  correlates  of  the  higher  affective  Ufe,  the  emotions 
and  esthetics.  It  has  often  been  pointed  out  that  the  conscious  processes 
resulting  from  exteroceptive  stimulation  tend  to  be  directed  outward,  the 
attention  being  focussed  on  the  external  objects  giving  rise  to  the  stimuU 
with  a  minimum  of  personal  reference.  The  deep  sensations,  both  of  the 
proprioceptive  and  the  interoceptive  group,  on  the  other  hand,  have  a  less 
clearly  defined  local  sign  and  the  mental  attitude  toward  them  is  not  one  of 
outwardly  directed  attention  to  the  source  of  the  stimulus,  but  rather  a 
change  in  the  subjective  state  and  an  alteration  of  the  general  feeling  tone 
of  the  body  as  a  whole.  Under  ordinary  circumstances  the  visceral  afferent 
and  other  deep  nervous  impulses  do  not  come  into  clear  consciousness  sepa- 
rately, but  in  the  aggregate  these  complexes  (often  termed  as  a  whole  com- 
mon sensation)  profoundly  modify  the  general  mental  attitude  and  equihb^ 
rium.  The  generahzed  feelings  of  both  the  pleasurable  and  the  painful  type 
share  this  subjective  reference  with  the  common  sensations.  They  are  very 
important  factors  in  that  sensory  continuum  which  hes  at  the  basis  of  the 
maintenance  of  personal  identity  which  the  older  psychologists  sometimes 
called  the  empirical  ego.  Only  the  pains  associated  with  the  sharply  local- 
ized cutaneous  sensation  qualities  with  a  high  adaptive  value  as  warning 
signs  of  external  danger  have  a  distinct  peripheral  reference,  and  even  this  is 
less  clearly  defined  than  that  of  the  accompanj^ing  sensations  of  pressure, 
and  so  forth.  The  deep  pains  are  imperfectly  localized  and  have  more  of  the 
general  subjective  reference  which  has  just  been  mentioned,  and  all  of  the 
pleasurable  quahties  are  of  this  type. 

The  simpler  affective  t^-pes  of  experience,  accordingly,  seem  to  be  most 
intimately  associated  with  the  "common  sensation"  complex,  especially 
with  the  visceral  sensation  components  of  this  complex.  From  this  it  has 
been  argued  that  the  coarser  emotions,  as  well  as  the  elementary  feeUngs,  are 
the  direct  expression  in  consciousness  of  these  visceral  activities,  that  the 
well-knowm  visceral  changes  associated  with  the  emotions  are  not  the  results, 
but  the  causes  of  the  emotions  (Lange  and  James).  This  hATDothesis  has 
been  attacked  experimentally  by  Sherrington  (see  The  Integrative  Action 
of  the  Nervous  Sj^stem,  1906,  p.  260),  who  found  that  cutting  the  afferent 
sjTnpathetic  fibers  from  the  abdominal  \-iscera  in  dogs  made  no  apparent 
difference  in  the  emotional  reactions  of  the  animals;  but  the  experiments  are 
not  very  convincing,  and  the  question  is  probably  too  complex  for  solution 
by  so  sunple  means  as  those  here  emploA'ed. 

The  probability  is  that  we  have  here  a  circular  type  of  reaction.  The 
initial  visceral  afferent  impulses,  being  heavily  charged  with  affective  quali- 


260  INTRODUCTION  TO  NEUROLOGY 

ties  and  with  a  minimum  of  objective  reference,  excite  within  the  brain, 
probably  in  the  medial  thalamic  nuclei,  a  general  non-localized  pleasurable 
or  unpleasant  feeling,  a  feeling  of  well-being  or  malaise,  as  the  case  may  be. 
These  thalamic  receptive  centers  are  in  very  intimate  relation  with  the 
visceral  efferent  systems  of  the  hypothalamus  and  a  reflex  response  in  the 
viscera  follows — a  typical  organic  circuit.  So  long  as  this  circuit  involves 
only  the  viscera  and  their  thalamic  centers  the  peripheral  reference  will  be  at 
a  minimum,  and  the  feeling  remains  an  unlocalized  change  in  the  affective 
consciousness. 

The  higher  emotional  and  esthetic  activities  are  so  charged  with  intellec- 
tual content  also  as  to  require  the  participation  of  the  association  centers  of 
the  cerebral  cortex.  But  no  pleasure-pain  centers  are  known  in  the  cortex 
and  the  evidence  at  present  available  seems  to  negative  the  presence  of  such 
centers.  The  agreeable  or  disagreeable  components  of  the  higher  emotional 
processes  are  very  probably  due  to  the  colligation  of  thalamic  activities 
with  cortical  associational  processes.  In  case  these  emotional  or  esthetic 
processes  are  of  cortical  origin,  that  is,  excited  in  the  first  instance  by  the 
activity  of  cortical  associational  centers,  their  affective  content  may  be  due 
to  the  involvement  of  the  subcortical  pleasure-pain  apparatus  in  the  asso- 
ciational process,  and  this  apparatus  would,  as  above  described,  generate 
efferent  impulses  from  the  related  visceral  centers,  thus  causing  the  charac- 
teristic visceral  movements,  which  in  turn  would  reinforce  the  visceral  activ- 
ities of  the  brain  centers,  and  thus  by  a  "back-stroke"  action  strengthen 
the  emotional  content  of  the  primary  associational  complex.  Thus  the  com- 
pletion of  the  circular  reaction  may  reinforce  the  affective  consciousness  so 
long  as  it  is  operative. 

That  pleasure  i?  correlated  with  free  discharge  of  nervous  energy  is  sug- 
gested further  by  the  fact  that  in  most  of  the  pleasurable  emotions  and  senti- 
ments there  is  present  a  large  factor  of  recall  of  previous  experiences.  The 
esthetic  enjoyment  of  a  given  situation  is  in  large  measure  proportional  to 
the  wealth  of  associated  memories  incorporated  within  it,  especially  when 
these  are  recombined  into  new  patterns.  The  pleasure  experienced  in  listen- 
ing to  a  complicated  musical  production  like  a  symphony  may  be  enhanced 
many  fold  after  one  has  become  thoroughly  familiar  with  it,  and  still  more 
so  if  the  listener  has  himself  played  it  or  parts  of  it. 

In  concluding  this  discussion  of  pleasure-pain  we  quote  the  following 
paragraph  from  Sherrington's  account  of  Cutaneous  Sensations,  already 
referred  to  (Schafer's  Physiology,  1900,  vol.  ii,  p.  1000) : 

"Affective  tone  is  an  attribute  of  all  sensation,  and  among  the  attribute 
tones  of  skin  sensation  is  skin-pain.  Affective  tone  inheres  more  intensely 
in  senses  which  refer  to  the  body  than  in  those  which  refer  to  the  environ- 
ment, that  is,  it  is  strongest  in  the  non-pro jicient  senses.  It  is,  therefore, 
strong  in  the  cutaneous  senses,  and  in  them  is  inversely  as  their  projicience, 
therefore  least  in  touch  spots,  more  in  thermal  spots,  most  in  the  so-called 
'pain-spots.'  .  .  .  Stimuli  evoking  skin-pain  are  broadly  such  as  injure 
or  threaten  injury  to  the  skin;  the  skin  may  be  said  to  have  gone  far  toward 
developing  a  special  sense  of  its  own  injuries.  The  central  conducting 
path  concerned  with  these  skin  feelings  seems  a  side-path  into  which  the 
impressions  from  the  various  skin  spots  embouch  with  various  ease,  those 
from  the  'pain  spots'  especially  easily.  The  physiological  reactions  connected 
with  this  side-path  are  characterized  by  tendency  to  '  summation, '  tendency 
to  'collateral  irradiation,'  slow  culmination,  and  slow  subsidence.  They 
often  involve  with  their  own  activity  that  of  adjacent  sensory  channels  (as- 


PAIN    AND    PLEASURE  261 

sociate  pains,  referred  pains),  and  almost  invariably  of  motor  centers  of 
visceral,  facial,  and  other  muscles  of  expression  (emotional  discharge)." 
Our  own  view  is  in  harmony  with  that  expressed  in  this  paragraph  except 
that,  while  we  recognize  that  sensations  in  general  have  an  affective  tone, 
we  do  not  consider  that  affective  experience  is  to  be  regarded  as  essentially 
an  attribute  or  quale  of  sensation.  These  are  independent  variables  which 
are,  however,  usually  intimately  associated.  Each  has  its  own  mechanism. 
The  mechanism  of  every  sensation  is  a  localizable  system  of  tracts  and 
centers  as  expounded  in  the  preceding  chapters.  The  mechanism  of  the 
affective  experience  is  a  more  general  neural  attitude  or  physiological  phase, 
intimately  bound  up  with  the  visceral  reactions  peripherally  and  inte- 
grated centrally  in  the  thalamus. 

Summary. — In  the  human  organism  pain  appears  to  be  a  true 
sensation  with  its  own  receptors,  probably  with  independent 
peripheral  neurons  (in  some  cases  at  least),  and  certainly  with 
well  localized  conduction  paths  and  cerebral  centers,  these  cen- 
ters being  thalamic  and  not  cortical.  Pain  appears  to  be  closely 
related  neurologically  with  feelings  of  unpleasantness  and  pleas- 
antness, and  these,  in  turn,  with  the  higher  emotions  and  the 
affective  life  in  general.  The  intellectual  elements  in  the  higher 
emotions  and  sentiments  are,  of  course,  cortical,  and  in  nearly  all 
cases  the  affective  experience  probably  involves  a  highly  complex 
interaction  of  cortical  and  subcortical  activities.  Pleasantness 
and  unpleasantness  are  not  regarded  simply  as  attributes  of 
specific  sensory  processes  in  any  case,  but  rather  as  a  mode  of 
reaction  or  physiological  attitude  of  the  whole  nervous  system 
intimately  bound  up  with  certain  visceral  reactions  of  a  protec- 
tive sort  whose  central  control  is  effected  in  the  ventral  and  medial 
parts  of  the  thalamus.  These  parts  of  the  thalamus  form,  ac- 
cordingly, the  chief  integrating  center  of  the  nervous  reactions 
involved  in  purely  affective  experience.  This  mechanism  is 
phylogenetically  very  old,  and  in  lower  vertebrates  which  lack 
the  cerebral  cortex  it  is  adequate  to  direct  avoiding  reactions  to 
noxious  stimuli  and  seeking  reactions  to  beneficial  stimuli. 
With  the  appearance  of  the  cortex  in  vertebrate  evolution  these 
thalamic  centers  became  intimately  connected  with  the  associ- 
ation centers  of  the  cerebral  hemispheres,  and  an  intelligent 
analysis  of  the  feelings  of  unpleasantness  and  pleasantness  be- 
came possible.  As  a  final  step  in  the  development  of  the  pro- 
tective apparatus  the  peripheral  nerves  of  painful  sensibility, 
with  their  own  specific  conduction  paths  and  centers,  were  differ- 


262  INTRODUCTION  TO  NEUROLOGY 

entiated,  and  pain  takes  its  place  among  the  other  exteroceptive 
senses.  But  even  in  man  the  thalamic  and  visceral  mechanisms 
of  affective  experience  are  preserved  and  give  a  characteristic 
organic  background  to  the  entire  conscious  hfe.  In  the  normal 
man  these  mechanisms  may  function  with  a  minimum  of  cor- 
tical control,  giving  tlje  general  feeling  tone  of  well-being  or 
malaise,  or  they  may  be  tied  up  with  the  most  complex  cortical 
processes,  thus  entering  into  the  fabric  of  the  higher  sentiments 
and  affections  and  becoming  important  factors  in  shaping  human 

conduct. 

Literature 

Cannon,  W.  B.  1914.  Recent  Studies  of  Bodily  Effects  of  Fear,  Rage, 
and  Pain,  Jour.  Philos.  Psych.  Sci.  Methods,  vol.  xi,  pp.  162-165. 

— .  1914.  The  Interrelations  of  Emotions  as  Suggested  by  Recent 
Physiological  Researches,  Amer.  Jour.  Psychol.,  vol.  xxv,  pp.  256-282. 

— .  1914.  The  Emergency  Function  of  the  Adrenal  Medulla  in  Pain  and 
the  Major  Emotions,  Amer.  Jour.  Physiol.,  vol.  xxxiii,  pp.  356-372. 

— .  1915.  Bodily  Changes  in  Pain,  Hunger,  Fear,  and  Rage,  New  York, 
311  pages. 

Capps,  J.  A.  1911.  An  Experimental  Study  of  the  Pain  Sense  in  the 
Pleural  Membranes,  Arch.  Internal  Medicine,  vol.  viii,  pp.  717-733. 

Head,  H.,  and  Holmes,  G.  1911.  Sensory  Disturbances  from  Cerebral 
Lesions,  Brain,  vol.  xxxiv,  pp.  109-254. 

Head,  H.,  and  Thompson,  T.  1906.  The  Grouping  of  the  Afferent  Im- 
pulses Within  the  Spinal  Cord,  Brain,  vol.  xxix,  p.  537. 

Herrick,  C.  L.  1910.  The  Summation-irradiation  Theory  of  Pleasure- 
pain.  In  The  Metaphysics  of  a  Naturalist,  Bui.  Denison  University 
Scientific  Laboratories,  vol.  xv. 

Holmes,  S.  J.  1910.  Pleasure,  Pain,  and  the  Beginnings  of  Intelligence, 
Jour.  Comp.  Neur.,  vol.  xx,  pp.  145-164. 

James,  W.  1890.  The  Principles  of  Psychology,  New  York,  vol.  ii,  pp. 
442-485. 

— .  1894.  The  Physical  Basis  of  Emotions,  Psych.  Rev.,  vol.  i,  p.  516. 

Karplus,  J.  P.,  and  Kreidl,  A.  1914.  Ein  Beitrag  zur  Kenntnis  der 
Schmerzleitung  im  Rtickenmark,  nach  gleichzeitigen  Durchschneidungen 
beider  Riickenmarkshalften  in  verschiedenen  Hohen  bei  Katzen,  Pfliiger's 
Archiv,  Bd.  158,  pp.  275-287. 

Lange,  C.  1887.  Ueber  Gemiithsbewegungen.  Eine  Psycho-physio- 
logische  Studie,  Leipzig. 

Meyer,  Max.  1908.  The  Nervous  Correlate  of  Pleasantness  and  Un- 
pleasantness, Psych.  Rev.,  vol.  xv,  pp.  201-216.  292-322. 

Sherrington,  C.  S.  1900.  Cutaneous  Sensations,  in  Schafer's  Physi- 
ology, vol.  ii,  pp.  965-1001. 

— .  1906.  The  Integrative  Action  of  the  Nervous  System,  New  York. 

Watson,  J.  B.  1913.  Image  and  Affection  in  Behavior,  Jour.  Philos. 
Psych.  Sci.  Methods,  vol.  x.  pp.  421-428. 


CHAPTER  XIX    • 

THE     STRUCTURE     OF    THE     CEREBRAL    CORTEX 

The  preceding  pages  have  included  a  brief  chapter  on  some  of 
the  general  biological  principles  underlying  the  differentiation  of 
the  structure  and  functions  of  the  nervous  system,  some  general 
characteristics  of  the  nervous  tissues,  a  brief  survey  of  the 
structure  of  the  various  great  divisions  of  the  nervous  system, 
and  finally  an  analysis  of  the  more  important  sensori-motor 
reflex  circuits.  Nearly  all  of  the  mechanisms  hitherto  consid- 
ered are  concerned  with  the  innate  invariable  types  of  response 
represented  in  the  reflex  and  instinctive  life  of  the  organism 
(p.  31).  In  the  higher  mammals,  and  especially  in  man,  the 
individually  acquired  relatively  variable  types  of  action,  par- 
ticularly those  which  are  consciously  performed,  require  the 
cooperation  of  the  cerebral  cortex,  and  the  following  chapters 
will  be  devoted  to  a  consideration  of  the  cortex,  its  structure, 
functions,  evolution,  and  biological  significance. 

We  have  already  commented  (pp.  109, 215)  on  the  fact  that  the 
cerebral  cortex  appeared  later  in  vertebrate  evolution  than  most 
of  the  other  parts  of  the  brain,  and  that  in  general  it  serves  the 
individually  acquired  and  intelligent  functions,  in  contrast  with 
the  brain  stem  and  cerebellum,  which  contain  the  apparatus  for 
the  innate  activities  of  the  reflex  type.  The  primarj^  reflex 
centers  of  the  brain  stem  and  cerebellum,  accordingly,  are  some- 
times called  the  old  brain  (palseencephalon,  see  Fig.  45,  p.  114), 
while  the  cerebral  cortex  and  those  parts  of  the  brain  stem  which 
develop  as  subsidiary  to  the  cortex  (such  as  the  neothalamus,  p. 
163)  are  called  the  new  brain  (neencephalon).^ 

^  A  review  of  the  evolution  of  the  brain  and  the  phylogenetic  origin  of 
the  cerebral  cortex  would  he  beyond  the  limits  of  this  work,  for  the  hter- 
ature  upon  this  subject  is  very  extensive.  The  following  papers  ma\'  be 
consulted  in  the  present  context.  (See  also  the  bibhographies  on  pp. 
159,  223.) 

Herrick,  C.  Judson.  1910.  The  Evolution  of  Intelligence  and  Its 
Organs,  Science,  N.  S.,  vol.  xxxi,  pp.  7-18. 

Smith,  G.  Elliot.  1910.  The  Arris  and  Gale  Lectures  on  Some  Prob- 

263 


264 


INTRODUCTION   TO    NEUROLOGY 


In  the  embryologic  development  of  the  human  brain  the  cere- 
bral hemispheres  grow  out  as  lateral  pouches  from  the  anterior 
end  of  the  neural  tube  (Figs.  46-54,  pp.  116-121).  These  pouches 
are  hohow  and  the  cavities  within  them  are  the  lateral  ventricles 
(also  called  the  first  and  second  ventricles),  each  of  which  com- 
municates with  the  third  ventricle  of  the  thalamus  by  a  narrow 
opening,  the  interventricular  foramen  or  foramen  of  Monro. 

In  a  simply  organized  brain  like  that  of  the  frog  (Fig.  119)  the 
olfactory  bulb  forms   the  anterior  end  of  each  cerebral  hemi- 


Olfactory  nerve 
Olfactory  bulb 
Lateral  ventricle 
Corpus  striatum 
Lamina  terminalis 
Interventricular  foramen 
Third  ventricle 
Optic  lobe 
Cerebellum 
Fourth  ventricle 


Fig.  119. — Diagrammatic  representation  of  an  amphibian  brain  from 
which  the  roof  of  the  thalamus  and  cerebral  hemisphere  has  been  dissected 
off  on  the  right  side,  exposing  the  third  and  the  lateral  ventricles  and  the 
interventricular  foramen  (foramen  of  Monro).  The  membranous  roof  of 
the  fourth  ventricle  has  also  been  removed. 

sphere,  behind  which  the  massive  wall  contains  ventrally  the 
basal  olfactory  centers  (p.  218),  laterally  the  corpus  striatum 
(p.  168),  and  dorsally  the  cerebral  cortex  or  pallium  (which  has 


lems  Relating  to  the  Evolution  of  the  Brain,  The  Lancet  for  January  1,  15, 
and  22,  1910. 

Smith,  G.  Elliot.  1912.  The  Evolution  of  Man,  Report  of  the  Anthro- 
pological Section  of  the  British  Assoc,  for  the  Advancement  of  Science, 
Dundee  Meeting.  Printed  also  in  Nature  (London)  for  Sept.  26,  1912, 
and  in  the  Smithsonian  Report  (Washington)  for  1912,  pp.  553-572. 


THE    STRUCTURE    OF    THE    CEREBRAL    CORTEX  265 

been  removed  on  the  right  side  of  Fig.  1 19).  In  the  human  brain 
the  cerebral  cortex  is  so  greatly  enlarged  that  it  overlaps  all  other 
structures  of  the  hemisphere. 

The  anterior  end  of  the  early  neural  tube  is  an  epithelial 
plate,  the  terminal  plate  or  lamina  terminalis,  which  forms  the 
anterior  wall  of  the  third  ventricle  in  the  median  plane.  The 
position  of  this  plate  is  unchanged  throughout  all  subsequent 
stages  of  development  (Figs.  46-51,  pp.  116-119,  and  Fig.  119), 
though  the  cerebral  hemispheres  grow  forward  on  each  side  of  it, 
so  that  in  the  adult  brain  it  lies  deeply  buried  at  the  bottom 
of  the  great  longitudinal  fissure  which  separates  the  hemispheres. 

The  reflex  centers  of  the  two  sides  of  the  spinal  cord  and  brain 
stem  are  connected  by  transverse  bands  of  fibers  known  as 
commissures,  for  the  facilitation  of  bilateral  adj  ustments.  There 
is  an  extensive  series  of  ventral  commissures  crossing  below  the 
ventricle  in  the  floor  of  the  midbrain,  medulla  oblongata,  and 
spinal  cord,  and  several  smaller  dorsal  commissures  are  found 
above  the  ventricle.  In  the  diencephalon  there  is  a  large  ventral 
commissure  associated  with  the  optic  chiasma,  and  a  dorsal  com- 
missure, the  superior  or  habenular  commissure,  connecting  the 
habenular  bodies  of  the  epithalamus.  The  basal  parts  of  the 
cerebral  hemispheres  are  connected  by  the  anterior  commissure, 
whose  fibers  cross  in  the  lamina  terminalis  (Fig.  78,  p.  165),  and 
there  are  two  large  commissures  which  connect  the  cerebral 
cortex  of  the  two  hemispheres.  One  of  these,  the  corpus  callo- 
sum  (Figs.  52,  p.  119,  and  78,  p.  165),  connects  the  non-olfactory 
cortex  (neopalhum,  p.  217),  the  other  one,  the  hippocampal 
commissure,  connects  the  olfactory  cortex  (hippocampus). 
The  fibers  of  the  hippocampal  commissure  lie  under  the  posterior 
end  of  the  corpus  callosum  in  close  relation  with  the  fimbria 
(Figs.  78,  p.  165,  and  80,  p.  170). 

In  the  smaller  mammals  the  cerebral  cortex  is  smooth,  but  in 
the  larger  forms  it  is  more  or  less  wrinkled,  so  that  the  surface 
is  marked  by  gyri  or  convolutions  separated  by  sulci  or  fissures. 
A  more  highly  convoluted  cortical  pattern  is  found  in  large 
animals  than  in  smaller  ones  of  closely  related  species,  and  in 
animals  high  in  the  zoological  scale  than  in  lower  species;  but 
the  factors  which  have  determined  this  pattern  in  each  individual 
species  are  very  complex  (see  Kappers,  1913  and  1914).     The 


266 


INTRODUCTION   TO    NEUROLOGY 


primary  factor  in  the  higher  mammals  has  undoubtedly  been 
the  great  increase  in  the  superficial  area  of  cortical  gray  matter 
without  a  corresponding  enlargement  of  the  skull. 

The  human  cerebral  cortex  is  somewhat  arbitrarily  divided 
into  frontal,  temporal,  parietal,  and  occipital  lobes  (Fig.  120). 
These  lobes  have  no  special  functional  significance,  but  are  dis- 
tinguished merely  for  convenience  of  topographic  description. 
Some  of  the  more  important  gyri  and  sulci  are  named  on  Figs. 
52  and  54  (pp.  119  and  121).  Between  the  temporal  and  frontal 
lobes  and  under  the  lower  end  of  the  lateral  or  Sylvian  fissure  is 
a  buried  convolution,  the  island  of  Reil  (insula),  which  is  seen  in 
section  in  Figs.  79  and  80  (pp.  166  and  170) .  The  cortical  lobules 
which  cover  the  insula  are  called  opercula  (Fig.  54,  p.  121). 


OCCIPITAL 
LOBE 


Fig.  120. — The  lateral  aspect  of  the  human  brain,  illustrating  the  boundaries 
of  the  lobes  of  the  cerebral  cortex  (cf.  Fig.  54). 

The  walls  of  the  cerebral  hemispheres  in  the  cortical  region  are 
very  thick,  the  greater  part  of  this  thickness  being  occupied  by 
white  matter  composed  of  nerve-fibers  which  effect  various  types 
of  connection  with  the  neurons  of  the  cerebral  cortex.  The 
cortex  itself  is  composed  of  gray  matter  and  is  relatively  thin, 
its  inner  border  being  marked  by  a  broken  line  in  Figs.  79  and  80. 
The  subcortical  white  matter  contains  three  chief  classes  of 
fibers:  (1)  Corona  radiata  fibers  which  connect  the  cortex  with 
the  brain  stem  (Figs.  79,  80).  Most  of  these  fibers  pass  through 
the  internal  capsule  and  comprise  the  sensory  and  motor  pro- 
jection fibers  (pp.  165-169) ;  (2)  commissural  fibers  of  the  corpus 
callosum  and  hippocampal  commissure  (Figs.  79,  80) ;  (3)  associ- 
ation fibers,  which  connect  different  parts  of  the  cerebral  cortex 


THE    STRUCTURE    OF    THE    CEREBRAL    CORTEX 


267 


of  each  hemisphere.  Some  of  these  fibers  are  very  short,  passing 
between  adjacent  gyri  (arcuate  fibers,  or  fibrse  proprias,  j.-p., 
Fig.  121);  others  are  very  long  fibers,  forming  compact  fascicles 
which  can  easily  be  dissected  out  and  which  connect  the  impor- 
tant association  centers  of  the  cortex.  All  parts  of  the  cerebral 
cortex  are  directly  or  indirectly  connected  with  all  other  parts 
by  these  association  fibers,  so  that  no  region  can  be  regarded  as 
the  exclusive  seat  of  any  particular  cortical  function. 


str.  term. 
1. 1,  s. 


fun 


Fig.  121. — Diagram  illustrating  some  of  the  chief  association  tracts  of 
the  cerebral  hemisphere,  seen  as  projected  upon  the  median  surface  of  the 
right  hemisphere:  cin.,  cingulum;  f.l.i.,  fasciculus  longitudinalis  inferior; 
f.l.s.,  fasciculus  longitudinalis  superior;  f. occ.fr. inf.,  fasciculus  occipitq- 
frontahs  inferior;  f.p.,  arcuate  fibers;  f.lr.oc,  fasciculus  transversus  occipi- 
talis;/.ttnc,  fasciculus  uncinatus;  str.  term.,  stria  terminaUs. 

The  human  cortex  varies  in  thickness  in  different  regions  from 
about  4  mm.  in  the  motor  area  to  less  than  half  that  thickness  in 
some  other  parts.  When  cut  across  and  examined  in  the  fresh 
condition  it  shows  alternate  bands  of  light  and  dark  gray,  whose 
arrangement  varies  in  different  parts  of  the  hemisphere.  The 
light  bands  are  composed  of  myelinated  fibers  which  run  parallel 
with  the  surface.  There  are  typically  two  of  these  light  bands, 
the  outer  and  inner  stripes  of  Baillarger  (Fig.  122).  In  the 
visual  projection  area  (Figs.  130,  131,  area  17)  the  outer  stripe 


268  INTRODUCTION  TO  NEUROLOGY 

of  Baillarger  is  greatly  thickened  by  the  optic  projection  fibers, 
and  here  it  is  sometimes  called  the  line  of  Gennari.  The  por- 
tion of  cortex  exhibiting  the  line  of  Gennari  is  called  the  area 
striata. 

The  most  characteristic  neurons  of  the  cortex  are  pyramidal  in 
shape,  with  the  apex  directed  toward  the  outer  surface  of  the 
brain  and  prolonged  to  form  the  principal  dendrite.  Smaller 
dendrites  arise  from  other  parts  of  the  cell  body,  and  the  axon 
arising  from  the  base  of  the  cell  body  is  directed  inward  into  the 
white  matter  (Figs.  7,  8,  pp.  42,  44).  The  cortex  contains,  more- 
over, many  other  types  of  neurons,  some  of  irregular  shape  (poly- 
morphic or  multiform  cells)  and  many  whose  axons  are  short  and 


Fig.  122. — Sections  of  the  cerebral  cortex,  drawn  nearly  natural  size  and 
showing  the  naked-eye  appearance:  1  shows  the  layers  as  they  appear  in 
rnany  parts  of  the  cortex,  and  2  shows  the  appearance  of  a  section  from  the 
visual  cortex  (area  striata)  from  the  neighborhood  of  the  calcarine  fissure, 
with  the  conspicuous  hne  of  Gennari.     (After  Baillarger.) 

ramify  close  to  the  cell  body  without  leaving  the  cortex  itself 
(Fig.  9,  p.  44).  These  type  II  neurons  probably  assist  in  the 
summation  and  irradiation  of  stimuli  (see  p.  101).  Some  other 
types  of  neurons  are  shown  in  Fig.  123. 

Figure  124  illustrates  a  typical  arrangement  of  the  neurons  in 
the  postcentral  gyrus  (gyrus  centralis  posterior  of  Fig.  54,  p.  121). 
Most  of  the  neurons  here  shown  send  their  axons  inward  to 
participate  in  the  formation  of  the  white  matter  and  may  dis- 
charge their  nervous  impulses  into  remote  parts  of  the  brain. 
The  endings  of  the  afferent  nerve-fibers  which  effect  synaptic 
connection  with  the  neurons  here  shown  form  a  dense  entangle- 
ment of  fine  unmyelinated  fibers  between  the  dendrites  of  these 
neurons.     These  afferent  fibers  are  not  included  in  Fig.  124;  one 


THE  STRUCTURE  OF  THE  CEREBRAL  CORTEX 


269 


of  them  is  shown  in  Fig.  123  and  they  are  drawn  separately  in 
Fig.  125  as  they  appear  in  the  precentral  gyrus  (gyrus  centrahs 
anterior  of  Fig.  54).  These  afferent  fibers  may  be  either  sensory 
projection  fibers  or  association  fibers  from  other  parts  of  the 


?^.V 


Fig.  123. — Diagrammatic  illustration  of  the  arrangement  of  neurons  in 
the  cerebral  cortex  as  revealed  by  the  Golgi  method.  The  figure  is  copied 
from  Obersteiner  and  the  layers  are  numbered  differently  than  in  Brod- 
mann's  scheme,  Fig.  127.  Obersteiner's  layer  III  includes  layers  III,  IV, 
and  V  of  Brodmann.  The  arrows  indicate  the  direction  of  nervous  conduc- 
tion, and  the  axons  of  the  neurons  are  marked  by  a  cross,  x  ;  gl.,  laj^er  of  su- 
perficial neuroglia  cells;  m,  beginning  of  the  layer  of  white  matter;  12,  13, 
14,  and  15  mark  neuroglia  (glia)  cells;  the  other  numbers  designate  different 
types  of  neurons. 


cortex.  The  synapses  between  these  incoming  fibers  and  the 
neurons  of  the  cortex  among  which  they  end  are  of  various  types. 
Many  of  the  afferent  fibers  end  in  the  outermost  layer  of  the 
cortex  (layer  1  of  Figs.  123  and  124)  among  the  dendrites  of  the 


270 


INTRODUCTION   TO    NEUEOLOGY 


Fig.  124. — Section  from  the  cerebral  cortex  of  a  human  infant  from  the 
postcentral  gjTus  (gyrus  centrahs  posterior),  with  the  neurons  impregnated 
by  the  method  of  Golgi.  The  figure  is  taken  from  Ramon  y  Cajal's  His- 
tology of  the  Central  Nervous  System,  and  the  layers  are  numbered  accord- 
ing to  his  system.  Layer  1  corresponds  to  Brodmann's  first  layer  (Fig. 
127);  layer  2,  to  his  second  layer;  layers  3  and  4,  to  his  third  layer;  layer  5, 
to  his  fourth  layer;  layer  6,  to  his  fifth  layer;  and  layer  7,  to  his  sixth  layer. 


THE    STRUCTURE    OF    THE    CEREBRAL    CORTEX 


271 


pyramidal  cells  which  are  here  widely  expanded  (see  Fig.  8,  p. 
44);  others  end  in  dense  arborizations  which  closely  envelop 


Fig.  125. — Section  of  the  human  cerebral  cortex  from  the  precentral 
gyrus  (gjTus  centralis  anterior),  illustrating  the  free  endings  of  the  incoming 
fibers.  This  region  contains  a  large  number  of  cells  similar  to  those  sho^\^l 
in  Fig.  124;  but  none  of  the  cells  were  stained  in  this  preparation,  which  was 
prepared  by  the  method  of  Golgi.  At  a  and  b  are  seen  the  terminal  arbori- 
zation of  two  individual  fibers.  At  B  is  a  dense  entanglement  of  such  ter- 
minal arborizq^tions  around  the  cell  bodies  of  the  ])\Tamidal  neiu'ons  of  layer 
3  (Fig.  124).  C,  D,  and  E  illustrate  horizontally  diiected  nerve-fibers, 
from  which  the  terminal  arborizations  shown  in  the  upper  part  of  the 
figure  arise.     (After  Ram6n  y  Cajal.) 


272 


INTRODUCTION   TO    NEUROLOGY 


the  bodies  of  the  pyramidal  cells  (Fig.  126).  Still  others  twine 
around  the  dendrites  for  their  entire  length.  The  dendrites  of 
the  pyramidal  cells  are  very  rough  and  thorny,  and  these  thorns 
are  supposed  by  some  to  be  the  points  where  the  actual  synaptic 
connections  are  effected. 

Besides  the  lamination  caused  by  the  bands  of  tangential 
nerve-fibers  already  referred  to,  the  cell  bodies  themselves  are 
arranged  in  layers  whose  pattern  varies  in  different  parts  of  the 


Fig.  126. — Section  of  the  human  cerebral  cortex  from  the  precentral 
gyrus,  illustrating  the  details  of  the  terminal  arborizations  of  the  incoming 
fibers  (a)  in  the  form  of  a  closely  woven  f eltwork  of  fibers  (b,  c,  d)  around  the 
cell  bodies  of  the  large  pyramidal  cells  of  the  cortex.  The  cells  themselves 
are  not  stained  in  the  preparation,  but  their  outhnes  are  clearly  indicated 
by  the  pericellular  basket-work  by  which  they  are  enveloped.  (After 
Ramon  y  Cajal.) 


cortex.  Neurologists  enumerate  these  layers  differently.  Brod- 
mann,  who  has  studied  this  question  very  exhaustively,  enumer- 
ates six  primary  layers  which  in  most  parts  of  the  cortex  are 
arranged  essentially  as  shown  in  the  accompanying  diagram 
(Fig.  127).  The  six  layers  here  recognized  are  present  in  most 
but  not  in  all  parts  of  the  cortex.  In  the  different  regions  one  or 
more  of  these  layers  may  be  reduced,  enlarged,  or  subdivided; 
and  on  the  basis  of  these  differences  the  entire  cortex  has  been 


THE  STRUCTURE  OF  THE  CEREBRAL  CORTEX      273 

mapped  out  into  areas,  each  of  which  is  defined  by  the  arrange- 
ment of  the  layers  of  cortical  cells  and  fibers. 

Brodmann  (Figs.  128,  129)  divides  the  cerebral  hemisphere 
into  eleven  general  regions,  which  he  says  are  recognizable  more 
or  less  clearly  throughout  the  entire  group  of  mammals.  These 
are: 

1.  Regio  postcentralis  (tactile  region). 

2.  Regio  precentralis  (motor  region). 

3.  Regio  frontalis  (frontal  association  center). 

4.  Regio  insularis  (insula). 

5.  Regio  parietalis  (parietal  association  center). 

6.  Regio  temporalis  (auditory  region). 

7.  Regio  occipitalis  (visual  region). 

8.  Regio  cingularis  (supracallosal  part  of  limbic  lobe). 

9.  Regio  retrosplenialis  (postcallosal  part  of  limbic  lobe). 

10.  Regio  hippocampica  (gyi'us  hippocampi  and  hippocampus). 

11.  Regio  olfactoria  (uncus,  amygdala,  tuberculum  olfactorium). 

In  the  list  as  here  given  Brodmann's  names  of  the  regions  are 
given,  and  in  parenthesis  is  added  a  brief  description  of  each 
region.  Regions  8,  9,  10,  and  11  are  all  concerned  with  the 
olfactory  reactions,  though  region  8  only  to  a  small  extent. 
Region  11  is  only  in  part  cortical  (the  uncus);  the  other  parts 
of  this  region  are  subcortical  olfactory  centers.  The  specific 
sensory  and  motor  projection  centers  (see  p.  165)  lie  within  their 
respective  regions,  as  designated,  but  they  do  not  occupy  the 
whole  of  their  regions.  On  the  basis  of  the  arrangement  of  their 
cells  and  fibers  these  regions  are  further  subdivided  by  Brod- 
mann into  upward  of  50  areas  or  fields,  as  shown  in  Figs.  130 
and  131.  The  areas  are  less  uniformly  developed  in  different 
animals  than  are  the  general  regions,  though  many  of  them  are 
very  cdnstantly  present. 

Bolton,  Campbell,  Ramon  y  Cajal,  Vogt,  Elliot  Smith,  and 
many  others  have  investigated  the  lamination  of  the  cerebral 
cortex  in  man  and  other  mammals,  and  many  charts  similar  to 
those  here  presented  have  been  published.  The  conclusions 
reached  by  these  authors  do  not  agree  in  all  respects  (particu- 
larly in  the  number  of  areas  separately  recognized  and  the 
nomenclature  of  the  layers  of  cells  and  fibers  in  the  various 
regions) ;  nevertheless  there  is  a  sufficiently  close  general  agree- 
ment to  make  it  evident  that  there  is  a  definite  structural  patt(M-n 
18 


274 


INTRODUCTION   TO    NEUROLOGY 


a, 


••^     /I 


Fig.  127. — Diagram  of  the  arrangement  of  the  layers  of  cells  and  mye- 
hnated  nerve-fibers  in  the  cerebral  cortex,  according  to  Brodmann.  At  the 
left  of  the  figure  is  shown  the  arrangement  of  cells  as  shown  by  the  Golgi 
method,  in  the  middle  their  arrangement  as  shown  by  Nissl's  method,  and  at 
the  right  the  arrangernent  of  nerve-fibers  as  shown  by  Weigert's  method. 
/.  Lamina  zonahs,  or  plexiform  layer,  containing  tangential  nerve- 
fibers. 

//.  Lamina  granularis  externa,  or  layer  of  small  pyramidal  cells. 
III.  Lamina  pyramidahs,  or  layer  of  medium  and  large  pyramidal  cells. 


THE  STRUCTURE  OF  THE  CEREBRAL  CORTEX      275 

which  is  characteristic  of  the  several  cortical  regions  in  each 
species  of  mammals,  and  that  this  pattern  is  broadly  similar  in 
all  of  the  higher  members  of  this  group  of  animals. 

Data  derived  from  physiological  experiments  made  on  dogs, 
apes  and  other  animals,  and  from  the  study  of  pathological  hu- 
man brains  have  shown  also  that  the  difference  in  structural 
pattern  of  the  cortical  areas  is  correlated  with  differences  in 
the  functions  performed  by  them.  To  these  functional  ques- 
tions our  attention  will  next  be  directed. 

Summary. — The  cerebral  cortex  is  the  organ  of  the  highest 
individually  modifiable  functions,  particularly  those  of  the 
intellectual  life.  It  matures  late  in  both  phylogenetic  and  indi- 
vidual development,  and  therefore  has  been  called  the  neenceph- 
alon.  In  early '  developmental  stages  it  forms  the  roof  of  the 
lateral  ventricle  of  each  cerebral  hemisphere,  but  in  the  adult 
human  brain  it  is  so  enlarged  as  to  envelop  most  other  parts  of 
the  hemisphere.  The  cortex  of  the  two  hemispheres  is  con- 
nected by  commissural  fibers  in  the  corpus  callosum  and  the  hip- 
pocampal  commissure.  The  various  regions  of  each  hemisphere 
are  connected  by  a  complex  web  of  association  fibers,  and  some 
parts  of  the  cortex  are  connected  with  subcortical  regions  by 
projection  fibers.  The  sensory  projection  fibers  discharge 
among  the  neurons  of  the  sensory  projection  centers,  and  the 
motor  projection  fibers  arise  from  neurons  of  the  motor  projec- 
tion centers.  The  intervening  association  centers  are  connected 
with  the  projection  centers  and  with  each  other  by  very  intricate 
systems  of  association  fibers.  The  cortex  is  laminated  by  bands 
of  horizontally  arranged  nerve-fibers  and  by  an  arrangement  of 
its  cells  in  layers.  The  pattern  of  this  lamination  varies  in 
different  regions,  and  charts  of  these  structurally  defined  regions 
are  found  to  show  a  general  correlation  with  the  functionally 
defined  areas  as  physiologically  and  pathologically  determined. 

IV.  Lamina  granularis  interna,  or  inner  granular  layer,  containing  the 
medullated  fibers  of  the  external  hne  of  Baillarger  (in  the  visual  area  called 
the  stripe  of  Gennari). 

V.  Lamina  ganghonaris,  or  layer  of  large  cells,  containing  in  the  motor 
area  the  giant  pjTamidal  cells  or  Betz  cells,  from  which  the  fibers  of  the 
pyramidal  tract  arise,  and  containing  in  most  areas  the  medullated  fibers  of 
the  internal  line  of  Baillarger. 

VI.  Lamina  multiformis,  or  layer  of  polymorphic  cells. 


276 


INTRODUCTION   TO    NEUROLOGY 


Fig.  128. — The  chief  regions  of  the  human  cerebral  cortex  as  determined 
by  Brodmann  from  the  study  of  the  structural  arrangements  of  the  layers  of 
cells  and  fibers,  seen  from  the  left  side. 


Fig.  129. — The  chief  regions  of  the  cortex,  seen  from  the  median  side. 


THE  STRUCTURE  OF  THE  CEREBRAL  CORTEX 
6 


277 


Fig.  130. — The  detailed  subdivisions  of  the  cortical  regions  shown  in  Fig. 
128  as  determined  by  Brodmann,  seen  from  the  left  side.  Each  area  or 
field  which  is  here  designated  by  a  number  and  conventional  sj^mbols  has  a 
distinctive  lamination  of  its  cells  and  fibers. 


Fig.  131.— The  same  brain  shown  in  Fig.  130,  seen  from  the  median  side. 


278  INTRODUCTION  TO  NEUROLOGY 

Literature 

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Function,  Based  on  the  Clinico-pathological  Study  of  Mental  Disease, 
Brain,  vol.  xxxiii.  Part  129,  pp.  26-148. 

Bolton,  J.  S.,  and  Moyes,  J.  M.  1912.  The  Cytoarchitecture  of  the 
Cerebral  Cortex  of  a  Human  Fetus  of  Eighteen  Weeks,  Braiin,  vol.  xxxv. 

Brodmann,  K.  1907.  Die  Kortexgliederung  des  Menschen,  Jour.  f. 
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— .  1909.  Vergleichende  Lokalisationslehre  der  Grosshirnrinde,  Leipzig. 

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Campbell,  A.  W.  1905.  Histological  Studies  on  the  Localization  of  Cor- 
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Kappers,  C.  U.  a.  1913.  Cerebral  Localization  and  the  Significance  of 
Sulci,  Proc.  XVII  Intern.  Congress  of  Medicine,  London. 

— .  1914.  Ueber  das  Rindenproblem  und  die  Tendenz  innerer  Hirnteile 
sich  diu-ch  Oberflachen-Vermehrung  statt  Volumzunahme  zu  vergrosseren, 
Folia  Neuro-biologica,  Bd.  8,  pp.  507-531. 

Ramon  y  Cajal.  1900-1906.  Studien  iiber  die  Hirnrinde  des  Menschen, 
Leipzig. 

Smith,  G.  Elliot.  1907.  A  New  Topographical  Survey  of  the  Human 
Cerebral  Cortex,  Jour.  Anat.  and  Physiol.,  vol.  xli. 

VoGT,  O.  1903.  Zur  anatomischen  Ghederung  des  Cortex  Cerebri, 
Jour.  f.  Psych,  u.  Neurol.,  Bd.  2. 

— .  1904.  Die  Markreifung  des  Kindergehirns  wahrend  der  ersten  vier 
Lebensmonate  und  ihre  methodologische  Bedeutung,  Jena. 


CHAPTER  XX 

THE  FUNCTIONS  OF  THE  CEREBRAL  CORTEX 

The  greatest  diversity  of  view  has  prevailed  and  still  prevails 
regarding  the  method  of  cortical  function.  That  the  cerebral 
cortex  is  concerned  in  some  way  with  the  higher  conscious  func- 
tions is  clearly  shown  by  a  large  body  of  experimental  and 
clinical  evidence. 

The  partial  or  complete  removal  of  both  cerebral  hemispheres 
has  been  accomplished  in  various  species  of  animals,  from  fishes 
to  apes,  and  the  changes  in  behavior  carefully  studied.  In 
fishes  and  frogs  the  behavior  is  but  Httle  modified,  save  for  the 
loss  of  the  sense  of  smell,  if  the  thalamus  is  left  intact;  but  if  the 
thalamus  also  is  destroyed,  the  animal  loses  all  power  of  sponta- 
neous movement,  of  feeding  when  hungry,  etc.,  though  it  will  still 
react  to  some  strong  stimuli  in  an  apparently  normal  manner. 
The  fundamental  reflexes  of  the  spinal  cord  and  brain  stem  are 
but  little  modified  by  this  operation  in  frogs,  save  for  the  dis- 
turbance of  the  olfactory  and  visual  functions.  The  recent 
experiments  of  Burnett  have,  moreover,  shown  that  frogs  in 
which  the  cerebral  hemispheres  alone  have  been  removed  are 
somewhat  more  excitable  than  normal  frogs  (probably  due  to  the 
loss  of  cortical  inhibitions),  and  that  simple  associations  easily 
learned  by  normal  frogs  are  in  this  case  impossible. 

In  the  dog  the  loss  of  the  cerebral  hemispheres  alone  leaves  the 
animal  in  a  state  of  profound  idiocy,  though  here  also  all  of  the 
primary  sensori-motor  reflexes  (except  the  olfactory)  remain  if 
the  thalamus  is  uninjured,  and  one  such  animal  operated  on  by 
Goltz  lived  for  eighteen  months.  During  this  time,  however,  he 
had  to  be  artificially  fed,  for  he  had  lost  the  ability  to  recognize 
food  when  set  before  him,  nor  did  he  show  any  of  his  former  signs 
of  intelligence.  (These  experiments  are  summarized  in  Schiifor's 
Physiology,  vol.  ii,  pp.  698  ff.,  to  which  the  reader  is  referred  for 

279 


280  INTRODUCTION  TO  NEUROLOGY 

references  to  the  literature;  see  also  the  papers  by  Goltz,  Edinger, 
and  Holmes,  cited  in  the  appended  Bibliography.) 

Edinger  and  Fischer  report  the  case  of  a  boy  who  lived  three 
years  and  nine  months,  whose  brain  when  examined  after  death 
showed  total  lack  of  the  cerebral  cortex  with  no  other  important 
defects.  In  this  boy  there  was  practically  no  development  in 
sensory  or  motor  power  or  in  intelligence  from  birth  to  the  time 
of  his  death.  The  infant  fed  when  put  to  the  breast,  but  showed 
no  signs  of  hunger,  thirst,  or  any  other  sensory  process.  It  lay  in 
a  profound  stupor  and  during  the  first  year  of  life  made  no 
spontaneous  movements  of  the  limbs.  Until  the  time  of  death 
there  was  little  change  from  this  condition,  save  for  continual 
crying  from  the  second  year  on.  This  case  shows  that  the  reflex 
functions  of  the  human  brain  stem  are  normally  under  cortical 
control  to  a  much  greater  extent  than  are  those  of  any  of  the 
lower  animals,  and  that  the  absence  of  the  cortex  accordingly 
involves  a  more  profound  disturbance  of  the  subcortical  ap- 
paratus (see  p.  129). 

About  a  hundred  years  ago  Gall  and  Spurzheim  examined  the 
brain,  form  of  skull,  and  physiognomy  of  many  persons  whose 
mental  characteristics  were  more  or  less  fully  known,  and 
reached  very  definite  conclusions  regarding  the  localization 
within  the  brain  of  particular  mental  faculties,  such  as  benevo- 
lence, wit,  and  destructiveness;  they  claimed,  further,  that  the 
sizes  of  these  specific  parts  of  the  brain  (and  hence  their  relative 
physiological  importance)  can  be  determined  by  study  of  the 
external  configuration  of  the  skull.  Many  valuable  observations 
were  accumulated  by  these  men  and  their  followers,  but  the  data 
were  so  uncritically  used  and  the  psychological  basis  of  their 
generalizations  was  so  faulty  that  the  alleged  science  of  phrenol- 
ogy which  they  founded  is  now  wholly  discredited  and  is  pro- 
fessed today  only  by  ignorant  charlatans. 

The  great  popularity  of  phrenology  fifty  years  and  more  ago 
grew  out  of  the  fact  that  it  served  to  give  a  pseudoscientific 
character  to  methods  of  reading  character,  and  hence  of  forecast- 
ing the  future  formerly  claimed  by  astrologers  and  necromancers. 
Modern  psychology  recognizes  that  the  mind  cannot  be  sub- 
divided into  any  such  distinct  ''faculties"  as  the  phrenologists 
used,  and  modern  neurology  finds  no  basis  for  the  sharply 


THE    FUNCTIONS    OF    THE    CEREBRAL    CORTEX  281 

defined  localization  of  these  or  any  other  mental  functions,  in 
the  sense  that  a  specific  cortical  area  is  the  exclusive  organ  of  a 
particular  mental  element. 

As  a  reaction  against  the  crude  theories  of  Gall  and  Spurzhcim 
it  was  commonly  believed  up  to  the  year  1870  that  there  is  no 
definite  localization  of  functions  in  the  cerebral  cortex,  but  that 
the  cortex  functions  as  a  whole,  much  hke  the  cerebellar  cortex, 
with  no  clearly  defined  functional  areas.  This  view  and  modi- 
fications of  it  are  still  very  prevalent.  Goltz,  who  succeeded 
in  removing  all  of  both  cerebral  hemispheres  from  several  dogs, 
holds  that  different  psychic  functions  are  not  localizable  in  the 
cortex,  but  that  removal  of  cortical  areas  simply  diminishes 
general  intelligence  in  proportion  to  the  amount  of  cortex  re- 
moved. Even  total  removal  of  the  cortex,  in  his  opinion,  does 
not  completely  destroy  consciousness.  Many  physiologists 
have,  on  the  other  hand,  taught  that  particular  conscious  func- 
tions are  localized  in  definite  cortical  areas,  somewhat  after  the 
fashion  of  a  refined  and  modernized  phrenology,  and  this  view  is 
very  prevalent  among  clinical  neurologists. 

The  modern  period  of  study  of  cortical  functions  was  inaugu- 
rated by  a  chance  observation  on  the  battlefield.  During  the 
Franco-Prussian  war  an  army  surgeon,  Fritsch,  while  operating 
on  a  wounded  soldier,  applied  the  galvanic  electric  current  to  the 
exposed  surface  of  the  brain  and  observed  a  twitching  of  some  of 
the  muscles.  This  was  followed  immediately  by  experimental 
researches  upon  the  electric  excitability  of  the  cerebral  cortex 
of  dogs,  the  first  results  of  which  were  published  by  Fritsch  and 
Hitzig  in  1870.  They  showed  that  there  are  regions  in  the 
vicinity  of  the  central  sulcus  (fissure  of  Rolando,  cruciate  sulcus) 
whose  excitation  in  the  living  animal  is  followed  by  movements 
of  definite  groups  of  muscles  on  the  opposite  side  of  the  body. 

These  observations  have  been  followed  by  an  immense  number 
of  experimental  researches  on  various  animals  (the  animals 
being  anesthetized  during  the  experiments)  and  clinico-patho- 
logical  studies  of  the  human  brain,  whose  correlation  and  integra- 
tion have  proved  very  difficult.  The  most  careful  studies  have, 
however,  in  general  given  concordant  results.  Without  attempt- 
ing a  summary  of  these  investigations  here,  we  may  mention  the 
recent  investigations  of  Sherrington  on  the  chimpanzee,  whose 


282 


INTRODUCTION   TO    NEUROLOGY 


results  as  summarized  on  Fig.  132  may  be  accepted  as  fully  in 
accord  with  the  best  previous  experimental  work,  with  the 
anatomical  investigations  of  the  regional  differentiation  of  the 
cortex,  and  with  the  most  recent  clinical  studies.  The  corre- 
sponding areas  of  the  human  brain  are  seen  in  Fig.  133. 

Anus  and  vagina 
Toes 
Ankle    . 


Shoulder 
Elbow 


Ear  Eyelid  /'     / 
Nose 

of  jaw 
Opening  of  jaw 


Closure     / 


\ 

Sulcus  centralis 


Vocal  cords 


Mastication 


Fig.  132. — Brain  of  a  chimpanzee  seen  from  the  left  side  and  from 
above,  upon  which  the  cortical  areas  whose  excitation  causes  bodily  move- 
ments are  indicated  by  shading.  The  regions  shaded  by  vertical  lines  and 
marked  "  eyes  "  indicate  the  frontal  and  part  of  the  occipital  regions  which 
when  electrically  excited  cause  conjugate  movements  of  the  eyes.  The 
regions  shaded  with  stipple  comprise  the  motor  projection  centers  from 
which  the  fibers  of  the  pyramidal  tract  arise.  The  names  printed  large 
on  the  stippled  area  indicate  the  main  regions  of  the  motor  area;  the  names 
printed  small  outside  the  brain  indicate  broadly  by  their  pointing  lines 
the  relative  topography  of  some  of  the  chief  subdivisions  of  the  main 
regions  of  the  motor  cortex.  But  there  exists  much  overlapping  of  the 
motor  areas  and  of  their  subdivisions  which  the  diagram  does  not  attempt 
to  indicate.     (After  Griinbaum  and  Sherrington.) 


The  electric  or  mechanical  stimulation  of  each  one  of  the 
shaded  areas  of  Fig.  132  is  followed  by  the  contraction  of  a 
particular  group  of  muscles  on  the  opposite  side  of  the  body,  as 


THE    FUNCTIONS    OF    THE    CEREBRAL    CORTEX 


283 


designated  on  the  figure.  The  electrically  excitable  motor  cor- 
tex is  of  two  types,  marked  on  the  figure  by  stipple  and  vertical 
cross-hatching  respectively.  Stimulation  of  the  latter  areas  in 
the  frontal  and  occipital  lobes  calls  forth  conjugate  movements 
of  the  eyes,  and  the  physiological  characteristics  of  these  areas 
are  very  different  from  those  of  the  areas  in  the  precentral  gyrus, 
which  are  shaded  with  stipple.  This  gyrus  is  the  true  motor 
projection  center,  and  a  comparison  of  Figs.  132  and  133  with 
Fig.  130  shows  that  its  limits  coincide  tolerable  closely  with 


Fig.  133. — The  human  cerebral  hemisphere  seen  from  the  left  side,  upon 
which  the  functional  areas  of  the  cortex  are  indicated.  The  area  marked 
"motor  speech"  is  Broca's  convolution.     (From  Starr's  Nervous  Diseases.) 


area  4  of  Brodmann's  chart  of  the  anatomically  distinct  cortical 
areas,  including,  however,  a  part  of  the  cortex  farther  forward 
in  area  6. 

The  structure  of  the  cortex  in  the  precentral  motor  area 
(Brodmann's  area  4)  is  very  characteristic.  In  this  region  the 
fifth  layer  of  the  cortex  (see  Fig.  127)  contains  a  type  of  large 
pyramidal  cells  (giant  pyramids  or  Betz  cells)  which  are  found 
nowhere  else  in  the  brain.  From  these  cells  arise  most  of  the 
fibers  of  the  pramidal  tract    (tractus    cortico-spinalis) .     This 


284  INTEODrCTION  TO  NEUROLOGY 

connection  has  been  proved  in  several  ways  in  addition  to  the 
direct  physiological  experiments  bj^  electric  stimulation  already 
referred  to.  First,  if  this  area  of  the  cortex  (and  a  portion  of 
area  6  in  front  of  it)  is  destroyed,  the  entire  p^Tamidal  tract  vnW 
degenerate,  a  result  which  follows  from  the  destruction  of  no 
other  part  of  the  cortex.  Conversely,  if  the  pyramidal  tract  is 
interrupted,  the  giant  pjTamidal  cells  of  this  area  are  the  only 
neurons  of  the  cortex  to  give  clear  pictures  of  chromatolysis  of 
their  chromophilic  substance.  In  the  third  place,  these  giant 
cells  of  the  human  cortex  have  been  counted,  and  a  count  of  the 
numl^er  of  fibers  in  the  pyramidal  tract  shows  that  the  numbers 
are  in  tolerablj^  close  agreement  (nearly  80,000  on  each  side  of 
the  bod}").  Finally,  a  case  of  sclerotic  degeneration  involving 
almost  the  entire  cortex  has  been  described  by  Spielmeyer,  in 
which  these  giant  cells  and  the  fibers  of  the  pyramidal  tract  alone 
escaped  injury. 

The  sensory  projection  centers  of  the  cortex  have  also  been 
determined  physiologically,  though  their  limits  are  less  precisely 
known  than  are  those  of  the  motor  cortex.  The  olfactory 
receptive  area  has  already  been  mentioned  as  comprised  within 
the  archipallium  (hippocampus  and  hippocampal  g'^TUs,  see 
p.  217),  only  a  part  of  which  is  exposed  on  the  surface  of  the 
brain  (the  regio  hippocampica  of  Fig.  129;  areas  27,  28,  34,  35  of 
Fig.  131).  The  visual  projection  center,  which  receives  fibers 
from  the  thalamic  optic  centers  in  the  pulvinar  and  lateral  genic- 
ulate body  (pp.  165,  212),  is  in  the  occipital  region  (Fig.  129). 
Area  17  (Fig.  131)  appears  to  be  the  chief  center  for  the  recep- 
tion of  these  visual  projection  fibers,  though  the  adjacent  area  18 
participates  in  this  function,  these  areas  together  comprismg 
the  area  striata  of  the  cortex  (p.  268).  The  auditoiy  projection 
center  is  in  the  upper  part  of  the  temporal  lobe  (area  41,  and 
probably  to  some  extent  area  42  also,  of  Fig.  130).  The  tactual 
projection  center  lies  in  the  postcentral  region  (Fig.  128;  areas  1, 
2,  and  3  of  Fig.  130).  The  parts  of  the  cerebral  cortex  which  lie 
between  the  sensory  and  motor  projection  centers  which  have 
just  been  enumerated  are  the  association  centers  (see  pp.  287, 
290). 

Within  each  general  sensors^  sphere  there  is  a  focal  area  which 
is  exclusively  receptive  in  function,  such  as  area  17  (Fig.  131)  in 


THE    FUNCTIONS    OF    THE    CEREBRAL    CORTEX  285 

the  visual  sphere.  Each  of  these  focal  spheres  is  surrounded  by 
other  areas  which  receive  projection  fibers,  though  in  less 
abundance,  and  also  numerous  association  fibers  from  other 
parts  of  the  cortex.  These  marginal  fields  are,  therefore,  to  be 
regarded  as  association  centers,  each  of  which  is  under  the 
dominant  physiological  influence  of  the  adjacent  focal  projection 
center.  These  are  sometimes  called  visual  psychic,  auditory 
psychic  fields,  etc.,  after  the  adjacent  projection  centers;  but 
these  terms  are  objectionable  as  implying  the  old  phrenological 
notion  of  localization  of  specific  psychological  faculties. 

Each  sensory  projection  center  which  receives  afferent  fibers 
of  course  sends  out  association  fibers  to  other  parts  of  the  cortex. 
Some  of  these  fibers  may  be  very  short,  reaching  only  to  the 
adjacent  marginal  fields  (these  are  arcuate  fibers,  see  Fig.  121, 
f.p.);  other  much  longer  association  fibers  may  assist  in  forming 
the  great  associational  tracts  of  the  subcortical  white  matter. 
The  association  centers  themselves  are  likewise  connected  by 
fiber  tracts  of  bewildering  complexity,  so  that  every  part  of  the 
cerebral  cortex  is  in  direct  or  indirect  physiological  connection 
with  every  other  part.  All  of  these  parts  are,  therefore,  able  to 
influence  the  motor  centers  of  the  precentral  gyrus,  from  which 
alone  voluntary  motor  impulses  can  be  discharged  from  the 
cortex  to  the  lower  motor  centers  of  the  brain  stem  and  spinal 
cord. 

The  relations  of  the  tactual  and  somesthetic  sensory  projection  fibers  to 
the  postcentral  and  precentral  gyri  have  been  variously  described,  and  some 
further  consideration  of  the  functional  connections  of  these  fibers  may  here 
be  appropriate.  From  a  large  body  of  anatomical,  experimental,  and  cHnical 
evidence  it  was  formerly  assumed  that  the  cortical  motor  centers  are  co- 
extensive with  those  for  the  general  somatic  sensory  projection  systems  of 
cutaneous  and  muscular  sensibility,  the  projection  centers  of  both  the 
sensory  and  motor  fibers  related  to  each  region  of  the  body  being  located 
on  both  the  anterior  and  posterior  sides  of  the  central  sulcus  or  fissiu-e  of 
Rolando,  that  is,  in  both  the  precentral  and  postcentral  gjTi.  Most  of  the 
diagrams  of  cortical  localization  in  all  but  the  most  recent  manuals  are 
based  upon  this  view  of  the  case.  But  recent  work  has  shown  definitely 
that  the  motor  centers  are  confined  to  the  region  in  front  of  this  sulcus. 
Here  only  are  found  the  giant  pyramidal  cells  of  Betz  which  give  rise  to 
most  of  the  fibers  of  the  pyramidal  tract.  It  may,  therefore,  be  regarded  as 
definitely  estab fished  that  motor  projection  fibers  do  not  arise  from  the 
postcentral  gyrus,  as  formerly  supposed. 

Sensory  projection  fibers,  however,  are  known  to  pass  from  the  general 
somatic  sensory  centers  in  the  ventral  and  lateral  nuclei  of  the  thalamus  to 


286  INTRODUCTION  TO  NEUROLOGY 

the  postcentral  gyrus,  to  the  motor  cortical  centers  of  the  precentral  gyrus, 
and  to  other  widely  separated  parts  of  the  cortex.  The  significance  of  this 
fact  is  still  obscure.  That  the  postcentral  gyrus  is  of  different  functional 
type  from  the  precentral  gyrus  is  shown  by  the  fact  that  motor  projection 
fibers  arise  from  the  latter  and  not  from  the  former,  by  the  differences  in 
anatomical  structure  of  these  regions,  by  a  large  amount  of  experimental 
and  clinical  evidence  which  shows  that  tactile  sensibihty  is  not  lost  by  the 
destruction  of  the  precentral  motor  areas,  and  finally  by  direct  physiological 
experiment  upon  human  subjects. 

Dr.  Harvey  Gushing  (1909),  in  operating  upon  brain  tumors  in  2  cases  in 
which  the  use  of  an  anesthetic  was  prohibited  by  the  condition  of  the  patient, 
exposed  the  postcentral  gyrus  and,  with  the  patient's  consent,  electrically 
stimulated  its  surface.  The  patients,  who  were  fully  conscious  during  the 
operation,  reported  distinct  cutaneous  sensations  which  were  subjectively 
localized  as  if  coming  from  the  skin  of  the  hand.  There  were  no  motor 
responses  from  this  and  adjacent  parts  of  the  cortex  behind  the  central 
sulcus,  though  in  the  same  cases,  upon  stimulation  of  the  precentral  gyrus, 
motor  responses  were  obtained  which  were  accompanied  by  no  sensations 
save  those  which  came  from  the  muscles  during  their  contraction.  In  a 
previous  similar  case  Dr.  Gushing  (1908)  obtained  typical  motor  responses 
from  stimulation  (with  the  patient's  consent)  of  the  precentral  gyrus  in  an 
operation  without  anesthesia,  and  these  responses  were  unaccompanied  by 
painful  sensations. 

A  very  extensive  series  of  experiments  involving  the  stimulation  and 
extirpation  of  these  cortical  areas  in  apes,  dogs,  and  other  animals  supports 
the  conclusion  that  the  postcentral  gjTus  is  the  great  receptive  center  for 
cutaneous  reactions  of  the  general  cutaneous  system.  What  may  be  the 
functions  of  those  thalamic  fibers  which  pass  to  the  motor  centers  in  front 
of  the  central  fissure  is  unsettled.  Possibly  these  connections  are  concerned 
in  cortical  reflexes  of  the  proprioceptive  system  or  acquired  automatisms. 

The  myelinated  fibers  of  the  cerebral  hemisphere  mature, 
that  is,  acquire  their  myehn  sheaths,  at  various  stages  in  the 
development  of  the  brain,  some  of  these  systems  of  fibers  appear- 
ing before  birth  and  some  after  birth.  Much  investigation  has 
been  directed  to  the  determination  of  the  exact  facts  regarding 
the  sequence  of  development  of  these  fibers,  and  many  interest- 
ing theories  have  been  developed  regarding  the  significance  of 
these  facts. 

Flechsig  in  a  long  series  of  researches  made  the  first  thorough  study  of 
this  problem,  and  his  conclusions  have  exerted  a  profound  influence  upon 
aU  subsequent  theories  of  the  functions  of  the  cerebral  cortex.  He  proposed 
a  series  of  laws  of  developmental  sequence  (myelogeny)  of  the  cortical  fibers, 
among  which  two  may  be  mentioned:  (1)  The  myehnated  fiber  tracts  of  the 
brain  do  not  aU  mature  at  the  same  time,  and  fiber  systems  which  are  of 
Uke  function,  that  is,  which  are  so  connected  as  to  perform  special  move- 
ments in  response  to  excitation,  tend  to  mature  at  the  same  time.  This  is 
Flechsig's  "fundamental  myelogenetic  law,"  which  may  be  stated  in  this 
form,  The  myelination  of  the  nerve-fibers  of  the  developing  brain  follows 


THE  FUNCTIONS  OF  THE  CEREBRAL  CORTEX      287 

a  definite  sequence  such  that  the  fibers  belonging  to  particular  functional 
systems  mature  at  the  same  time.  (2)  A  second  law  states  that  in  the 
cerebral  cortex  there  are  two  great  functional  groups  of  fibers  which  mature 
at  different  times.  One  of  these  groups  contains  the  projection  fibers,  which 
mature  early,  chiefly  before  birth ;  the  other  group  contains  the  association 
fibers,  which  mature  after  birth.  These  groups  are  further  subdivided  into 
subsidiary  functional  systems,  each  of  which  connects  with  a  definite  region 
of  the  cerebral  cortex,  so  that  it  is  possible  to  map  the  cortical  areas  in  ac- 
cordance with  the  sequence  of  development  of  the  related  myelinated  fibers. 
There  are,  accordingly,  two  groups  of  cortical  areas  in  this  scheme:  the 
projection  centers  whose  fibers  mature  early  and  the  association  centers 
whose  fibers  mature  late. 

Figures  134  and  135  illustrate  the  arrangement  of  these  areas,  the  prim- 
ary areas  (projection  centers)  being  marked  by  double  cross-hatching  and 
the  association  centers  by  single  cross-hatching  or  unshaded  areas.  The 
numbers  printed  on  the  charts  indicate  the  approximate  order  in  which 
the  corresponding  parts  acquire  their  myelinated  fibers.  It  will  be  noticed 
that  Flechsig's  projection  areas  do  not  correspond  exactly  with  those  deter- 
mined by  the  physiological  method  and  by  the  histological  study  of  the  adult 
cortex  (Figs.  130,  131,  132,  133). 

On  the  basis  of  his  studies,  Flechsig  elaborated  a  highly  speculative 
theory  of  the  significance  of  the  association  centers,  which  has  been  criticized 
as  a  return  to  the  old  attempt  to  localize  particular  mental  functions  in 
definite  cortical  areas.  These  criticisms  are  not  wholly  justified;  never- 
theless it  is  even  yet  premature  to  attempt  so  detailed  an  analysis  of  the 
cortical  mechanisms  of  psychic  processes  as  Flechsig  has  elaborated.  His 
observations  on  the  facts  of  myelogeny,  moreover,  have  not  been  confirmed 
by  more  recent  students  of  the  question  (Monakow,  Vogt,  Dejerine,  and 
others),  though  it  seems  to  be  established  that  the  sensory  and  motor 
projection  centers  in  general  acquire  myelinated  fibers  earlier  than  other 
parts  of  the  cerebral  cortex.  (This  entire  question  is  criticallj^  reviewed 
by  Brodmann  in  Lewandowsky's  Handbuch  der  Neurologic,  Band  2,  pp. 
234-244.)  The  only  conclusion  at  present  possible  is  that  the  factors  which 
operate  in  determining  the  sequence  of  myelination  of  the  nerve-fibers  of 
the  brain  are  exceedingly  complex,  and  it  is  impossible  from  the  facts  at 
present  known  to  formulate  the  laws  of  the  myelogenetic  development  of 
the  brain. 

Attention  should  be  called  here  to  the  fact  that  there  are  many 
different  kinds  of  projection  fibers,  that  is,  fibers  connecting  the 
cerebral  cortex  with  the  underlying  structures  of  the  brain  stem 
and  spinal  cord.  Most  of  these  projection  fibers,  except  those 
of  the  olfactory  system,  pass  through  the  corona  radiata  and 
internal  capsule  of  the  corpus  striatum.  The  most  important 
of  these  projection  systems  are  the  great  sensory  radiations  which 
discharge  their  nervous  impulses  into  the  cortical  centers  of 
vision,  hearing,  touch,  and  smell,  as  already  described  (the 
exact  course  of  the  gustatory  projection  fibers  has  not  been  de- 
termined), and  the  great  motor  system  of  the  pyramidal  tract 


288 


INTRODUCTION   TO    NEUROLOGY 


Fig.  135. 

Figs.  134,  135. — Lateral  and  median  views  of  the  human  cerebral  hemi- 
sphere, to  illustrate  the  sequence  of  maturity  of  the  myelinated  fibers  of 
the  cortex  during  the  development  of  the  brain,  according  to  Flechsig's 
observations.  The  numbers  indicate  approximately  the  order  in  which 
different  parts  of  the  cortex  acquire  their  mature  fibers.  Areas  1-12 
(double  cross-hatched)  constitute  the  primordial  region,  made  up  chiefly 
of  the  projection  centers;  these  include  the  olfactory  area  (1,  3,  4,  and  4a), 


THE    FUNCTIONS    OF    THE    CEREBRAL    CORTEX  289 

arising  from  the  precentral  gyrus.  Each  of  the  thalamo-cortical 
projection  tracts  of  vision,  hearing,  and  tactile  sensibiUty  is, 
moreover,  accompanied  by  cortico-thalamic  fibers  which  conduct 
in  the  reverse  direction  and  whose  functions  are  not  well  known, 
and  there  are  other  cortico-thalamic  and  cortico-mesencephalic 
systems.  The  cerebral  cortex  is  in  direct  connection  with  the 
red  nucleus  of  the  cerebral  peduncle  by  a  cortico-rubral  tract, 
arising  in  the  frontal  region  of  the  cortex,  and  by  ascending 
fibers  from  the  red  nucleus  to  the  same  general  part  of  the 
cerebral  hemisphere.  From  the  frontal,  parietal,  temporal,  and 
occipital  association  centers  there  arise  large  descending  fiber 
tracts  to  the  nuclei  of  the  pons  (cortico-pontile  tracts).  These 
connections  between  the  cerebral  cortex  and  the  red  nucleus 
and  pons  put  the  cerebral  cortex  and  the  cerebellum  into  very 
intimate  relations,  but  the  exact  way  in  which  the  cerebrum  and 
the  cerebellum  cooperate  functionally  is  obscure  (see  p.  192). 

From  the  preceding  account  it  is  plain  that  the  cerebral  cortex 
is  structurally  differently  organized  in  different  parts,  and  that 
each  of  these  parts  has  its  own  characteristic  fiber  connections. 
Physiological  experiment  and  pathological  studies  have  shown, 
moreover,  that  some  of  these  regions,  the  projection  centers,  are 
functionally  diverse,  in  that  each  one  receives  a  particular  type 
of  afferent  fibers  or  discharges  efferent  impulses  into  a  definite 
subcortical  motor  center.  Stated  in  other  words,  the  cortex  is 
structurally  a  mosaic  of  diverse  patterns ;  and  on  the  physiolog- 
ical side  there  is  a  specific  localization  of  function,  at  least  in  the 
sense  that  the  various  systems  of  afferent  and  efferent  projection 
fibers  connect  each  with  its  particular  place  in  the  structural 
mosaic. 

Several  English  neurologists,  notably  Bolton,  from  studies  on  the 
development  and  adult  structure  of  the  cortex  in  normal  and  abnormal  men 
and  in  other  mammals,  have  been  led  to  the  conclusion  that,  in  addition  to 
the  mosaic  locaUzation  pattern  of  which  we  have  been  speaking,  there  is  a 
functional  difference  between  the  different  layers  of  neurons  of  the  cortex 

the  somesthetic  area  (2,  26,  2c,  and  S),  the  visual  area  (7  and  probably  7b), 
and  the  gustatory  area  (46  and  6).  The  remainder  of  the  cortex  is  made  up 
of  association  centers,  of  which  there  are  two  groups,  those  wliich  mature 
soon  after  birth  (hghtly  shaded  areas  13-28),  and  the  terminal  areas  (un- 
shaded areas  28-36)  which  are  the  last  to  mature.  (From  Lewandowsky's 
Handbuch  der  Neurologie.) 

19 


290  INTRODUCTION  TO  NEUROLOGY 

in  general.  Bolton  believes  that  the  granular  layer  (layer  IV  of  Fig.  127) 
marks  an  important  boundary  between  functionally  different  cortical 
mechanisms.  The  infragranular  portion  of  the  cortex  is  thought  to  be 
concerned  especially  with  the  performance  of  the  simpler  sensori-motor 
reactions,  particularly  those  of  the  instinctive  type,  while  the  supragranular 
layers  serve  the  higher  associations  manifested  by  the  capacity  to  learn  by 
individual  experience  and  to  develop  the  intellectual  life. 

The  infragranular  layers  mature  earUer  in  the  development  of  the  brain, 
and  they  are  the  last  to  suffer  degeneration  in  the  destruction  of  cortical 
ceUs  in  the  acute  dementias  or  insanities.  The  supragranular  layers 
(notably  the  pyramidal  neurons  of  Brodmann's  third  layer,  Fig.  127)  ma- 
ture later  than  any  other  layers.  They  are  thinner  in  lower  animals  and  in 
feeble-minded  and  imbecile  men  than  in  the  normal  man,  and  they  are  the 
first  to  show  degenerative  changes  in  dementia. 

This  doctrine  is  controverted  by  some  other  neurologists,  but  the  evi- 
dence seems  to  show  that  the  supragranular  pjrramidal  neurons  are  physio- 
logically the  most  important  elements  in  the  higher  associative  processes  of 
the  cortex.  In  this  connection  it  is  significant  that  the  granular  and  infra- 
granular layers  are  thicker  in  the  projection  centers,  while  in  the  association 
centers  the  supragranular  layers  of  pyramidal  cells  are  thicker.  But  all  of 
the  layers  in  each  region  are  very  intimately  related,  the  processes  of 
most  of  the  cells  of  the  deeper  layers  extending  throughout  the  thickness  of 
the  more  superficial  layers  (see  Figs.  123, 124, 125)  to  reach  the  most  super- 
ficial layer,  and  in  the  present  state  of  our  knowledge  a  functional  differ- 
ence between  the  layers  cannot  be  said  to  have  been  estabhshed,  save  in 
very  general  terms. 

It  must  be  borne  in  mind  that  tlie  most  significant  parts  of 
the  human  cerebral  cortex  are  the  association  centers.  These 
alone  are  greatly  enlarged  in  the  human  brain  as  compared  with 
those  of  the  higher  apes.  In  the  latter  animals  the  projection 
centers  are  fully  as  large  as  those  of  man,  the  much  smaller 
brain  weight  being  chiefly  due  to  the  relatively  poor  develop- 
ment of  the  association  centers. 

The  data  which  we  have  summarized  in  the  preceding  pages 
have  led  to  the  most  contradictory  theories  as  to  the  exact 
mode  of  functioning  of  the  association  centers.  Neurologists 
have  been  prone,  even  up  to  the  present  time,  to  fall  into  the 
error  of  attempting  to  find  specific  centers  for  particular  mental 
functions  or  faculties.  But  the  evidence  at  present  available 
gives  small  promise  of  success  in  the  search  for  such  centers. 
It  is,  in  fact,  theoretically  improbable  that  such  discoveries  will 
ever  be  made,  for  psychology  today  recognizes  no  such  mosaic 
of  discrete  mental  facultie;S  as  would  be  implied  in  such  a  doc- 
trine. 

The  facts  of  cerebral  localization  as  clinically  and  experi- 


THE    FUNCTIONS    OF    THE    CEREBRAL    CORTEX  291 

mentally  demonstrated,  in  thjsmselves  and  aside  from  any  philo- 
sophic theories  based  upon  them,  contribute  no  evidence  what- 
ever to  a  solution  of  the  problem  of  a  seat  of  consciousness  or  of 
particular  mental  "faculties."  That  the  proper  functioning  of 
a  given  locus  in  the  cortex  is  essential  to  the  execution  of  a 
given  motion  or  the  experience  of  a  given  sensation  by  no  means 
necessarily  implies  that  the  consciousness  of  the  act  is  located 
there.  The  latter  is  an  entirely  independent  problem  which 
must  be  separately  investigated.  It  is  not,  then,  the  facts  of 
cerebral  localization  which  can  be  called  in  question  so  much  as 
the  interpretation  of  these  facts. 

The  search  for  a  single  seat  of  consciousness,  such  as  psychol- 
ogists and  philosophers  have  so  long  sought,  is  vain.  The  higher 
mental  processes  undoubtedly  require  the  activity  of  associa- 
tion centers  of  the  cerebral  cortex,  and  the  integrity  of  the 
associational  mechanism  as  a  whole  is  essential  for  their  full 
efficiency.  The  cerebral  cortex  differs  from  the  reflex  centers  of 
the  brain  stem  chiefly  in  that  all  of  its  parts  are  interconnected 
by  inconceivably  complex  systems  of  associational  connections, 
many  of  which  are  probably  acquired  late  in  life  under  the  influ- 
ence of  individual  experience,  and  any  combination  of  which 
may,  under  appropriate  conditions  of  external  excitation  and 
internal  physiological  state,  become  involved  in  any  cerebral 
process  whatever. 

Nevertheless,  some  of  these  cortical  association  paths  are 
structurally  more  highly  elaborated  than  others  (Fig.  121,  p. 
267,  illustrates  the  most  distinct  of  these  tracts),  and  certain 
combinations  of  cortical  functions  are,  therefore,  more  likely  to 
follow  a  given  stimulus  than  others.  This  associational  pattern 
is  doubtless  partly  innate  and  partly  acquired.  That  there  is  a 
fairly  precise  anatomical  pattern  of  association  tracts  can  be  seen 
in  any  good  dissection  of  the  cerebral  hemisphere,  and  that  the 
elements  of  this  pattern  are  related  in  definite  functional  systems 
which  are  spatially  separate  is  shown  by  numberless  clinical  ob- 
servations in  which  sharply  circumscribed  mental  defects  are 
found  to  be  associated  with  definite  cerebral  lesions.  The 
phenomena  of  aphasia  give  the  clearest  illustrations  of  these 
relations. 

The  term  aphasia  has  commonly  been  applied  to  a  variety  of 


292  INTRODUCTION  TO  NEUROLOGY 

speech  defects,  but  Hughlings  Jackson  extended  the  connotation 
of  the  word  to  include  "a  loss  or  defect  in  symbolizing  relations 
of  things  in  any  way."  The  lesion  which  produces  the  defect 
affects  the  association  centers  rather  than  the  projection  centers, 
for  there  is  no  primary  sensory  defect — no  blindness  or  deafness 
or  loss  of  general  sensation — nor  is  there  any  motor  paralysis. 
The  problems  connected  with  aphasia  are  very  difficult  and 
confused,  and  there  is  by  no  means  general  agreement  on  either 
the  fundamental  physiological  mechanisms  involved  in  speech  or 
on  the  nature  of  the  lesions  which  produce  the~  various  types  of 
observed  speech  defects.  The  enormous  literature  relating  to 
this  subject  cannot  be  summarized  here;  see  the  text-books  of 
physiology,  physiological  psychology,  and  clinical  neurology. 

Lesions  of  the  primary  sensory  or  motor  projection  centers  will  not  pro- 
duce aphasia,  for  in  these  cases  all  sensations  or  all  movements  related  'to 
the  injured  parts  are  lost,  whereas  in  aphasia  only  the  correlations  involved 
in  speech  or  other  associational  processes  are  impaired  and  all  other  sensori- 
motor correlations  may  be  intact.  Of  course,  the  mmiber  of  associational 
pathways  involved  in  the  communicating  of  ideas  by  hearing,  reading, 
speaking,  and  writing  words  is  very  large;  and  the  character  of  the  speech 
defect  will  depend  in  part  upon  the  particular  associational  tracts  affected 
by  the  lesion  and  in  part  upon  the  effect  of  the  lesion  upon  the  general  in- 
telligence of  the  patient  (diaschisis  effect,  see  p.  293).  The  second  factor 
seems  to  be  exceedingly  variable  and  has  given  rise  to  much  controversy. 

Distinctive  names  have  been  given  to  the  more  important  types  of  speech 
defect  as  clinically  observed ;  such  as  agraphia  or  inability  to  write  correctly, 
aphemia  or  inability  to  utter  words,  word-blindness  (alexia)  or  inability  to 
comprehend  written  words,  word-deafness  or  inability  to  comprehend 
spoken  words,  and  many  others.  Evidently  an  aphasia  may  result  from 
injury  to  (1)  a  sensory  association  area  contiguous  to  the  primary  visual  or 
auditory  projection  centers  (sensory  types  of  aphasia),  or  (2)  to  a  motor 
association  center  contiguous  to  the  motor  projection  centers  for  the  speech 
muscles  (motor  types),  or  (3)  to  any  of  the  associational  tracts  connecting 
these  association  centers. 

The  second,  or  motor,  type  of  aphasia  usually,  though  not  invariably, 
results  from  injury  to  the  posterior  part  of  the  inferior  frontal  gyrus  (see 
Fig.  54,  p.  121)  of  the  left  hemisphere  in  right-handed  persons  and  of  the 
right  hemisphere  in  left-handed  persons.  This  relation  was  first  discovered 
by  Br  oca,  and  the  area  of  motor  speech  correlations  (marked  "motor  speech" 
in  Fig.  133,  p.  283)  has  since  been  termed  Broca's  convolution. 

It  should  be  reiterated  that  Broca's  convolution  does  not  lie  in  the  excit- 
able motor  zone  of  the  cortex.  Though  the  destruction  of  this  area  may  be 
followed  by  defects  of  speech,  the  muscles  of  the  larynx,  tongue,  lips,  etc., 
involved  in  vocalization  are  not  paralyzed.  This  case  is  typical  of  many 
other  motor  association  centers  of  the  cortex  whose  integrity  is  essential  for 
specific  motor  combinations,  though  separate  motor  centers  are  present  for 
aU  of  the  muscles  involved  in  these  movements. 


THE  FUNCTIONS  OF  THE  CEREBRAL  CORTEX      293 

The  correlations  involved  in  the  motor  functions  of  speech  appear  to  be 
represented  typically  in  only  one  hemisphere,  though  this  is  by  no  means 
rigidly  true.  The  corresponding  structures  in  the  other  hemisphere  may 
cooperate  in  these  functions  normally,  and  after  loss  of  speech  from  a  uni- 
lateral lesion  speech  maj'  be  reacquired  by  further  education  of  the  unin- 
jured centers  of  the  same  or  the  opposite  side.  It  has  recently  been  shown 
that  Broca's  convolution  is  often  larger  on  the  left  side  of  the  brain  than  on 
the  right  side  and  that  the  average  thickness  of  the  cortex  in  this  region  is 
greater  on  the  left  side. 

^'arious  attempts  have  been  made  to  locahze  each  of  the  various  tj^pes  of 
aphasia  mentioned  above  in  a  specific  part  of  the  cortex,  but  with  no  con- 
cordant results.  Each  of  these  functions  is,  of  course,  verj-  complex,  and  a 
smaU  cu'CUiBScribed  cortical  injur}'  may  distm-b  or  temporai'ily  abolish  the 
entire  complex  by  the  destruction  of  one  onlj'  of  the  component  functional 
connections.     (See  the  summary  by  Dr.  A.  Aleyer,  1910.) 

The  general  conclusion  to  be  drawn  from  the  entire  series  of 
physiological  and  pathological  studies  of  the  cortex  is  that  spe- 
cific mental  entities  are  not  resident  in  particular  cortical  areas, 
but  that  cortical  functions  involve  the  discharge  of  nervous  en- 
ergy from  one  or  more  sensory  centers  to  various  near  and  remote 
regions,  each  of  which,  in  turn,  may  serve  as  a  point  of  departure 
for  new  nervous  discharges,  and  so  on  until  the  complexity  of 
action  and  interaction  of  part  upon  part  becomes  too  intricate 
for  the  mind  to  conceive.  The  resultant  effect  of  all  of  these 
nerv^ous  activities  which  reverberate  from  one  association  center 
to  another  will  be  the  establishment  by  a  process  of  which  we  are 
still  in  ignorance  of  an  equilibrium,  usually  by  means  of  a  motor 
discharge  of  some  precise  form  from  the  cortex  through  the 
pjTamidal  tract. 

This  djTiamic  view  of  cortical  function  finds  a  further  illustra- 
tion in  the  realm  of  neuro-pathology  in  von  Monakow's  doctrine 
of  diaschisis.  The  onset  of  cerebral  hemorrhage  or  any  other 
sudden  injury  to  the  cerebral  cortex  is  usually  marked  by  an 
apoplectic  ''stroke,"  with  profound  shock  and  usually  loss  of 
consciousness.  The  entire  cortical  equilibrium  is  disturbed  and 
this  effect  irradiates  very  widely  throughout  the  nervous  system. 
If  the  injury  is  not  too  severe,  there  is  soon  a  partial  readjust- 
ment of  the  nervous  equilibrium  and  consciousness  returns.  But 
the  restoration  is  incomplete,  for  some  of  the  normal  factors 
in  the  d^^lamic  equilibrium  complex  are  lacking  by  reason  of  the 
destruction  of  the  corresponding  cortical  areas  or  association 
tracts.     The  intelligence  is  enfeebled  and  all  voluntarj^  control  is 


294  INTRODUCTION  TO  NEUROLOGY 

impaired.  In  the  course  of  a  few  weeks  or  months  a  new  equi- 
hbrium  minus  the  lacking  factors  is  estabhshed  and  the  patient 
very  rapidly  improves.  Ultimately  complete  recovery  may 
occur,  save  for  a  permanent  residual  defect  which  results  directly 
from  the  loss  of  the  tissue  destroyed. 

The  immediate  shock-like  interference  with  the  activity  of 
cerebral  centers  not  directly  affected  by  the  lesion  is  what  von 
Monakow  means  by  diaschisis.  Upon  the  restoration  of  the 
nervous  equilibrium  this  transient  diaschisis  effect  is  wholly  or 
partially  lost,  and  the  residual  symptoms  of  defect  give  a  fairly 
accurate  picture  of  the  intrinsic  functions  of  the  center  directly 
attacked  by  the  lesion.  It  is  commonly  assumed  that  there 
is  also  during  the  process  of  gradual  recovery  from  such  a  corti- 
cal injury  a  certain  capacity  for  the  compensatory  development 
of  other  centers  of  the  same  or  the  opposite  cerebral  hemisphere, 
so  that  they  learn  to  perform  vicariously  the  functions  of  the 
lost  part. 

All  functions  of  the  nervous  system  are  facilitated  by  repeti- 
tion, and  many  such  repetitions  lead  to  an  enduring  change  in 
the  mode  of  response  to  stimulation  which  may  be  called  physio- 
logical habit.  This  implies  that  the  performance  of  every  reac- 
tion leaves  some  sort  of  a  residual  change  in  the  structure  of  the 
neuron  systems  involved.  These  acquired  modifications  of 
behavior  are  manifested  in  some  degree  by  all  organisms  (see 
pp.  22,  31),  and  this  capacity  lies  at  the  basis  of  all  associative 
memory  (whether  consciously  or  unconsciously  performed)  and 
the  capacity  of  learning  by  experience.  This  modifiability 
through  individual  experience  is  possessed  by  the  cerebral  cortex 
in  higher  degree  than  by  any  other  part  of  the  nervous  system; 
and  the  capacity  for  reacting  to  stimuli  in  terms  of  past  experi- 
ence as  well  as  of  the  present  situation  lies  at  the  basis  of  that 
docility  and  intelligent  adaptation  of  means  to  ends  which  are 
characteristic  of  the  higher  mammals.  It  is  a  fact  of  common 
observation  that  those  animals  which  possess  the  capacity  for  in- 
telligent adjustments  of  this  sort  have  larger  association  centers 
in  the  cerebral  cortex  than  do  other  species  whose  behavior  is 
controlled  by  more  simple  reflex  and  instinctive  factors,  that  is, 
by  inherited  as  contrasted  with  individually  acquired  organiza- 
tion.    This  is  brought  out  with  especial  distinctness  by  a  com- 


THE    FUNCTIONS    OF    THE    CEREBRAL    CORTEX  295 

parison  of  the  brains  of  the  higher  apes  with  that  of  man  (Figs. 
132,  133),  and  of  the  lower  races  of  men  as  contrasted  with  the 
higher.  In  our  own  mental  life  we  recognize  the  persistence  of 
traces  of  previous  experience  subjectively  as  memory,  and  mem- 
ory lies  at  the  basis  of  all  human  culture.  From  this  it  follows 
that  psychological  memory  is  probably  a  function  of  the  associa- 
tion centers;  but  it  must  not  be  assumed  that  specific  memories 
reside  in  particular  cortical  areas,  much  less  that  they  are  pre- 
served as  structural  traces  left  in  individual  cortical  cells,  as  has 
sometimes  been  done.^ 

The  simplest  concrete  memory  that  can  appear  in  conscious- 
ness is  a  very  complex  process,  and  probably  involves  the  activity 
of  an  extensive  system  of  association  centers  and  tracts.  That 
which  persists  in  the  cerebral  cortex  between  the  initial  experi- 
ence and  the  recollection  of  it  is,  therefore,  in  all  probability  a 
change  in  the  interneuronic  resistance  such  as  to  alter  the 
physiological  equilibrium  of  the  component  neurons  of  some 
particular  associational  system.  What  the  nature  of  this  change 
may  be  is  unknown,  but  it  is  conceivable  that  it  might  take  the 
form  of  a  permanent  modification  of  the  synapses  between  the 
neurons  which  were  functionally  active  during  the  initial  experi- 
ence such  as  to  facilitate  the  active  participation  of  the  same 
neurons  in  the  same  physiological  pattern  during  the  reproduc- 
tion. 

That  which  we  know  subjectively  as  the  association  of  ideas 
may,  in  a  somewhat  similar  way,  be  pictured  as  involving  neuro- 
logically  the  discharge  of  nervous  energy  in  the  cortex  between 
two  systems  of  neurons  which  have  in  some  previous  experience 
been  physiologically  united  in  some  cortical  reaction.  If,  for 
instance,  I  heard  a  song  of  a  mocking  bird  for  the  first  time  lasb 
year  while  walking  in  a  rose  garden,  upon  revisiting  the  gar- 
den I  may  recall  the  song  of  the  bird.  Here  the  sight  of  the 
garden  (a  highly  complex  apperceptive  process  involving  many 
association  tracts)  actuates  neuron  system  number  one  domi- 
nated by  present  visual  afferent  impulses,  and  the  association 

^  These  residua  of  past  cerebral  activities  form  the  basis  of  those  char- 
acteristic "brain  dispositions"  which  arc  important  factors  in  each  person- 
ahty.  They  have  been  termed  "engrams"  by  Semonand  "neurograms"  by 
Morton  Prince  (see  Prince,  The  Unconscious,  Chapter  V,  New  York,  1914). 


296        ■     INTRODUCTION  TO  NEUROLOGY 

tract  leading  to  neuron  system  number  two  (the  auditory  com- 
plex established  last  year  when  the  song  was  heard)  has  a  lowered 
physiological  resistance  by  virtue  of  the  previous  collocation 
with  system  number  one^  and  I  remember  the  song  (see  p.  64). 
It  should  be  emphasized  that  the  mechanism  of  association 
here  suggested  is  purely  theoretical;  we  have  no  scientific  evi- 
dence regarding  the  details  of  such  physiological  processes.  But 
it  can  be  confidently  asserted  that  even  the  simplest  associational 
processes  are  at  least  as  complex  as  this,  and  may  involve  the 
participation  of  thousands  of  neurons  in  widely  separate  parts  of 
the  cortex;  and  the  consciousness  must  be  regarded  as  a  function 
of  the  entire  process,  not  of  any  detached  center  (cf.  p.  66). 

In  summarizing  this  dynamic  conception  of  the  nature  of  consciousness  I 
will  quote  a  few  sentences  from  my  brother's  writings  (see  C.  L.  Herrick, 
1910,  pp.  13,  14): 

"The  theory  of  consciousness  which  seems  best  to  conform  to  the  condi- 
tions of  brain  structure  and  its  observed  unity  is  that  each  conscious  state  is 
an  expression  of  the  total  equilibrium  of  the  conscious  mechanism,  and  that 
intercurrent  stimuh  are  continually  shifting  the  equilibrium  from  one  to 
another  class  of  activities.  In  other  words,  the  sensation  accompanying 
a  given  color  presentation  is  not  due  to  the  vibrations  in  the  visual  center 
in  the  occipital  lobe,  but  to  the  state  of  cortical  equilibrium  or  the  equation 
of  cortical  excitement  when  that  color  stimulus  predominates.  Previous 
vestigeal  excitements  and  coordinations  [associations,  c.  j.  h.,  see  p.  35] 
with  the  data  from  other  cortical  centers  all  enter  into  the  conscious  pres- 
entation. As  the  wave  of  excitation  passes  from  the  visual  center  to  other 
parts,  the  proportional  participation  of  other  centers  increases,  producing  a 
composite  containing  more  distantly  related  elements." 

"Every  specific  sense-content  with  its  escort  of  reflexly  produced  associ- 
ated elements  causes  a  more  or  less  profound  disturbance  of  the  psychical 
equilibrium,  and  the  nature  of  this  disturbance  depends  not  only  on  the 
intensity  and  state  of  concentration,  but  very  largely  on  the  kind  of  equi- 
Ubrium,  already  existing.  .  .  .  The  character  of  the  conscious  act  (and 
the  elements  of  consciousness  are  always  acts)  will,  of  course,  depend  upon 
the  extent  to  which  the  several  factors  in  the  associational  system  partici- 
pate in  the  equilibrium.  Each  disturbance  of  the  equilibrium  spreads  from 
the  point  of  impact  in  such  a  way  that  progressively  more  of  the  possible 
reflex  currents  enter  the  complex,  thus  producing  the  extension  from  mere 
sensation  to  the  higher  processes  of  apperceptive  association.  A  conscious 
act  is  always  a  fluctuation  of  equilibrium,  so  that  all  cognitive  elements 
are  awakened  in  response  to  changes  rather  than  invariable  or  monotonous 
stimuli." 

The  dynamic  view  of  consciousness  here  adopted  makes  such 
expressions  as  "the  unconscious  mind"  impossible  contradic- 
tions.    Either  the  mental  functions  are  in  process  or  they  are 


THE    FUNCTIONS    OF   THE    CEREBRAL    CORTEX  297 

not,  and  unconscious  cerebration  is  not  consciousness.  This  is, 
of  course,  not  incompatible  with  a  dissociation  of  consciousness 
into  multiple  or  co-conscious  units,  as  Dr.  Morton  Prince  so 
forcibly  illustrates  (The  Unconscious,  p.  249),  though  how 
far  in  normal  men  this  dissociation  may  be  carried  is  an  open 
question. 

In  my  life  as  viewed  by  an  outside  observer  there  is  continu- 
ity of  process,  but  not  necessarily  continuity  of  consciousness. 
In  my  own  experience  consciousness  appears  to  be  continuous,  of 
course,  because  the  periods  of  unconsciousness  (as  in  coma,  deep 
sleep,  etc.)  do  not  appear  in  consciousness;  that  is,  they  do  not 
exist  for  me  except  as  I  learn  of  them  by  an  indirection.  In  a 
water  mill  the  function  of  grinding  corn  may  go  on  intermittently, 
though  the  mechanism  is  there  all  the  time  and  the  energy  is 
there;  but  if  the  water  passes  from  the  mill  race  out  over  the  dam 
instead  of  through  the  water  wheel  the  grinding  function  ceases. 
While  the  mill  is  at  rest  changes  may  be  made  in  the  machinery 
which  will  modify  the  character  of  the  grinding  when  it  is  re- 
sumed, but  these  changes  are  not  grinding.  So  in  the  brain  the 
mechanism  of  consciousness  and  the  structural  memory  vestiges 
of  past  experience  may  be  present  continuously;  indeed,  these 
vestigeal  traces  may  be  linked  up  in  new  ways  by  intercurrent 
physiological  processes.  But  these  things  do  not  constitute  con- 
sciousness. In  fact,  a  large  amount  of  unconscious  cerebration 
may  go  on,  the  end  result  of  which  alone  becomes  conscious. 
The  aim  of  physiological  psychology  is  to  clarify  not  only  the 
mechanism  of  consciousness,  but  also  all  of  the  antecedent  and 
subsequent  physiological  processes  which  are,  from  the  stand- 
point of  an  outside  observer,  demonstrably  related  to  the  con- 
scious processes.  It  is  possible,  moreover,  to  develop  a  really 
scientific  introspective  psychology  in  which  abstraction  is  made 
from  all  of  these  mechanisms  and  the  individual  experiences 
alone  are  studied  as  given  in  consciousness.  This  makes  up  a 
large  part  of  general  psychology. 

Summary. — The  functions  of  the  cerebral  cortex  are  still 
largely  wrapped  in  mystery,  but  the  evidence  thus  far  accumu- 
lated suggests  that  these  functions  are,  so  far  as  physiologically 
known,  not  different  in  kind  from  those  of  the  other  parts  of  the 
brain.     It  is,  however,  manifest  that  these  functions  are  con- 


298  INTRODUCTION  TO  NEUROLOGY 

cerned  with  the  individually  acquired  and  especially  the  intelli- 
gently performed  activities  as  distinguished  from  the  fundamen- 
tal reflex  and  instinctive  processes  whose  mechanisms  are  innate. 
There  is  a  specific  localization  of  function  in  the  cerebral  cortex, 
in  the  sense  that  particular  systems  of  sensory  projection  fibers 
terminate  in  special  regions  (the  sensory  projection  centers), 
that  from  other  special  regions  (the  motor  projection  centers) 
particular  systems  of  efferent  fibers  arise  for  connection  with  the 
lower  motor  centers  related  to  groups  of  muscles  concerned  with 
the  bodily  movements,  and  that  between  these  projection  centers 
there  are  association  centers,  each  of  which  has  fibrous  connec- 
tions of  a  more  or  less  definite  pattern  with  all  other  parts  of  the 
cortex.  The  destruction  of  any  part  of  the  cortex  or  of  the 
fiber  tracts  connected  therewith  involves,  first,  a  permanent  loss 
of  the  particular  functions  served  by  the  neurons  affected,  and, 
in  the  second  place,  a  transitory  disturbance  of  the  cortical 
equilibrium  as  a  whole  (diaschisis  effect).  Specific  mental  acts 
or  faculties  are  not  resident  in  particular  cortical  areas,  but  all 
conscious  processes  probably  require  the  discharge  of  nervous 
energy  throughout  extensive  regions  of  the  cortex,  and  the  char- 
acter of  the  consciousness  will  depend  in  each  case  upon  the 
dynamic  pattern  of  this  discharge  and  the  sequence  of  function  of 
its  component  systems.  This  pattern  is  inconceivably  complex 
and  only  the  grosser  features  are  at  present  open  to  observation 
by  experiment  and  pathological  studies. 

No  cortical  area  can  properly  be  described  as  the  exclusive 
center  of  a  particular  function.  Such  ''centers"  are  merely 
nodal  points  in  an  exceedingly  complex  system  of  neurons  which 
must  act  as  a  whole  in  order  to  perform  any  function  whatsoever. 
Their  relation  to  cerebral  functions  is  analogous  to  that  of  the 
railway  stations  of  a  big  city  to  traffic,  each  drawing  from  the 
whole  city  its  appropriate  share  of  passengers  and  freight;  and 
their  great  clinical  value  grows  out  of  just  this  segregation  of 
fibers  of  like  functional  systems  in  a  narrow  space,  and  not  to  any 
mysterious  power  of  generating  psychic  or  any  other  special 
forces  of  their  own. 

The  essence  of  cortical  function  is  correlation,  and  a  cortical 
center  for  the  performance  of  a  particular  function  is  a  physio- 
logical absurdity,  save  in  the  restricted  sense  described  above,  as 


THE    FUNCTIONS    OF    THE    CEREBRAL    CORTEX  299 

a  nodal  point  in  a  very  complex  system  of  associated  conduction 
paths.  Those  reflexes  whose  simple  functions  can  be  localized 
in  a  single  center  have  their  mechanisms  abundantly  provided  for 
in  the  brain  stem.  The  resting  brain  is  probably  normally 
during  life  in  a  state  of  neural  tension  in  more  or  less  stable 
equilibrium.  An  effective  stimulus  disturbs  this  equilibrium 
and  the  precise  effect  will  depend  upon  variable  synaptic  resist- 
ance or  neuron  thresholds  which  change  with  different  functional 
states  of  the  organism  as  a  whole  and  of  the  brain  in  particular. 
If  this  activity  involves  the  cerebral  cortex  of  a  human  brain,  it 
may  be  a  conscious  activity,  the  kind  of  consciousness  depending 
on  the  kind  of  discharge.  But  the  consciousness  must  not  be 
thought  of  as  localized  in  any  cortical  area.  The  discharge  in 
question  may  reverberate  to  the  extreme  limits  of  the  nervous 
system  and  the  peripheral  activities  may  be  as  essential  in  deter- 
mining the  conscious  content  as  the  cortical. 

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Burnett,  T.  C.  1912.  Some  Observations  on  Decerebrate  Frogs,  with 
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Gushing,  H.  1908.  Removal  of  a  Subcortical  Cystic  Tumor  at  a  Second- 
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— .  1909.  A  Note  upon  the  Faradic  Stimulation  of  the  Postcentral  Gyrus 
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Edinger,  L.  1893.  The  Significance  of  the  Cortex  Considered  in  Con- 
nection with  a  Report  Upon  a  Dog  from  which  the  Whole  Cerebrum  had 
been  Removed  by  Professor  Goltz,  Jour.  Comp.  Neurol,  vol.  iii,  pp.  69-77. 

— .  1908.  The  Relations  of  Comparative  Anatomy  to  Comparative 
Psychologv,  Jour.  Comp.  Neurol.,  vol.  xviii,  pp.  437-457. 

Edinger,  L.,  and  Fischer,  B.  1913.  Ein  Mensch  ohne  Grosshirn,  .Arch, 
f.  ges.  Phy.siol.,  Bd.  152,  pp.  1-27. 

Flechsig,  p.  1896.  Gehirn  und  Seele,  Leipzig. 

— .  1896.  Die  Lokalisation  der  geistigen  Vorgange,  Leipzig. 

Fkanz,  S.  I.  1915.  Variations  in  Distribution  of  the  Motor  Centers, 
Psychological  Monographs,  Princeton,  N.  J.,  vol.  xix.  No.  1,  pp.  80-162._ 

Fritsch,  G.,  and  Hitzig,  E.  1870.  Ueber  die  elektrische  Erregbarkeit 
des  Grosshirns,  Arch.  f.  Anat.,  Physiol,  u.  ^^'issen.  Mod.,  p.  300. 

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Nerveux,  Paris. 

GoLTZ,  F.  1869.  Beitrage  zur  Lehre  von  den  Functionon  der  Nerven- 
centren  des  Frosches,  Berhn. 


300  INTRODUCTION  TO   NEUROLOGY 

GoLTZ,  F.  1892.  Der  Hund  ohne  Grosshirn,  Arch.  f.  ges.  Physiol.,  Bd. 
51,  p.  570. 

Grunbaum,  a.  S.  F.,  and  Sherrington,  C.  S.  1903.  Observations  on  the 
Physiology  of  the  Cerebral  Cortex  of  the  Anthropoid  Apes,  Proc.  Roy.  Sob., 
vol.  Ixxii,  p.  152. 

Head,  H.,  and  Holmes,  G.  1911.  Sensory  Disturbances  from  Cerebral 
Lesions,  Brain,  vol.  xxxiv,  pp.  109-254. 

Herrick,  C.  L.  1910.  The  Equihbrium  Theory  of  Consciousness,  in 
The  Metaphysics  of  a  Naturalist,  Bui.  Sci.  Lab.  Denison  University,  vol. 
XV,  pp.  12-22. 

Hitzig,  E.  1904.  Physiologische  und  kUnische  Untersuchungen  iiber 
das  Gehirn,  Berlin. 

Holmes,  G.  W.  1901.  The  Nervous  System  of  the  Dog  Without  a 
Forebrain,  Jour.  Physiol.,  vol.  xxvii. 

Lewandowsky,  M.  1907.  Die  Funktionen  des  zentralen  Nervensys- 
tems,  Jena. 

Marie,  P.  1906.  Revision  de  la  Question  de  I'Aphasie,  Semaine  Med- 
icale,  23  May. 

Meyer,  A.  1910.  The  Present  Status  of  Aphasia  and  Apraxia,  The 
Harvey  Lectures  for  1909-10,  New  York,  pp.  228-250. 

VON  MoNAKOW,  C.  1909.  Neue  Gesichtspunkte  in  der  Frage  nach  der 
Lokalisation  im  Grosshirn,  Zeits.  f.  Psychologie,  Bd.  54,  pp.  161-182. 

— .  1910.  Aufbau  und  Lokalisation  der  Bewegungen  beim  Menschen. 
Arbeiten  a.  d.  hirnanatom,  Institut  in  Zurich,  Bd.  5,  pp.  1-37;  also  in  Bericht 
iiber  den  IV  Kongress  f.  exp.  Psychologie  in  Innsbruck,  1910. 

— .  1913.  Theoretische  Betrachtungen  liber  die  Lokahsation  in  Zentral- 
nervensystem,  insbesondere  im  Grosshirn,  Ergebnisse  der  Physiol.,  Bd.  13, 
pp.  206-278. 

— .  1914.  Die  Lokalisation  im  Grosshirn.  Gegenwartiger  Stand  der 
Frage  der  Lokalisation  in  der  Grosshirnrinde,  Wiesbaden. 

MuNK,  H.  1890.  Ueber  die  Funktionen  der  Grosshirnrinde.  Gesam- 
melte  Abhandl.,  2d  ed.,  Berlin. 

— .  1902.  Zur  Physiologic  der  Grosshirnrinde,  Arch.  f.  Physiol.,  1902. 

Prince,  M.  1914.  The  Unconscious,  New  York. 


CHAPTER  XXI 

THE  EVOLUTION  AND  SIGNIFICANCE  OF  THE  CERE- 
BRAL  CORTEX 

At  the  conclusion  of  our  analysis  of  the  structure  and  func- 
tions of  the  nervous  system  it  will  be  of  interest  to  review  very 
briefly  a  few  topics  of  a  more  general  sort  related  to  our  theme, 
with  special  reference  to  the  significance  of  the  cerebral  cortex 
in  the  general  scheme  of  human  evolution  and  culture. 

For  the  purpose  of  our  analysis  animal  activities  may  be 
classified  under  three  heads  (see  p.  31):  (1)  Innate  functions  of 
invariable  or  stereotyped  character  developed  through  natural 
selection  or  other  biological  processes,  whose  mechanism  is  hered- 
itary and  common  (with  small  differences  only)  to  all  members  of 
a  race  or  species,  typified  by  reflex  action  and  purely  instinctive 
action;  (2)  variable  and  modifiable  functions,  whose  pattern  is 
determined  by  individual  experience  through  which  the  innate 
action  system  is  more  or  less  permanently  altered,  intelhgent 
acts  and  the  reasoning  process  representing  the  highest  forms  of 
this  type,  though  the  lower  members  of  this  series  are  not  neces- 
sarily consciously  performed;  (3)  acquired  automatisms,  or 
individually  acquired  actions  which  have  become  so  thoroughly 
habitual  as  to  be  performed  quite  as  mechanically  as  the  heredi- 
tary reflexes.  Intelligently  acquired  actions  which  have  finally 
come  to  be  automatically  and  even  unconsciously^  performed  are 
sometimes  designated  "lapsed  intelHgence,"  but  such  lapsed 
intelligence  must  be  a  purely  individual  acquisition.  There 
is  no  evidence  that  automatisms  of  this  sort  can  be  transmitted  in 
heredity,  and,  therefore,  they  can  play  no  part  directly  in  the 
evolution  of  instincts,  as  some  have  taught. 

The  first  and  second  of  the  types  of  action  above  distinguished 
appear  to  be  common  to  all  organisms,  though  their  relative  im- 
portance varies  enormously  from  species  to  species.  The  first 
type  includes  the  reflexes  and  all  of  the  pure  instinct-actions, 

301 


302  INTRODUCTION  TO  NEUROLOGY 

that  is,  the  hereditary  component  of  the  commonly  recognized 
instincts  (p.  61).  There  is  no  clear  boundary  between  reflexes 
and  instinct-actions  as  just  defined.  These  actions  may  be 
exceedingly  complex  and  their  neuro-muscular  mechanisms  may 
be  complicated  apparently  without  limit.  The  available  evi- 
dence suggests  that  they  are  always  unconsciously  performed. 

Most  of  our  common  activities  include  all  three  of  these  types 
of  behavior  in  varying  proportions,  and  accordingly  they  fre- 
quently have  not  been  distinguished.  The  first  and  third  types 
are  especially  liable  to  confusion,  for  both  are  manifested  as 
stereotyped,  non-intelligent  behavior.  They  can  sometimes  be 
separated  only  by  a  study  of  their  origins;  nevertheless  this  dis- 
tinction is  of  great  importance,  especially  to  educators. 

The  nervous  organs  of  the  invariable  reactions  are  fairly  well 
known  and  are  characterized  in  their  more  highly  elaborated 
forms  by  a  closely  knit  system  of  nerve-centers  and  distinct  con- 
necting fiber  tracts  so  organized  that  particular  stimuli  may  call 
forth  a  response  or  a  combination  of  several  responses  selected 
from  a  fixed  number  of  possible  actions.  The  range  of  possible 
reactions  of  any  given  functional  system  of  this  type  is  limited 
by  the  structural  complexity  of  the  nerve-centers  involved. 
This  complexity  may  be  very  great,  with  a  correspondingly  great 
number  of  movements  necessary  to  complete  the  reaction,  and  it 
may  include  the  capacity  for  discriminating  between  two  or  more 
structurally  possible  modes  of  response  by  means  of  variable 
internal  functional  states  of  the  nerve-centers.  But  in  all  of 
these  cases  the  response  is  finally  determined  within  rather  nar- 
row limits  by  the  nature  of  the  stimuli  and  the  innate  structural 
organization  not  only  of  the  nervous  organs,  but  of  the  body  as  a 
whole. 

In  some  cases  an  elaborate  nervous  reflex  or  instinctive  act 
may  involve  a  more  extensive  nervous  apparatus  than  is  required 
by  an  intelligent  act.  It  is  not  a  mere  question  of  the  size  of  the 
nervous  mechanisms  involved.  For  instance,  a  comparison  of 
the  brains  of  the  two  species  of  fishes  shown  in  Fig.  136  shows 
that  in  the  medulla  oblongata  of  these  rather  closely  related 
species  there  is  an  astonishing  difference  between  the  size  of 
certain  reflex  centers.  The  greater  size  of  the  medulla  oblon- 
gata of  Carpiodes  over  that  of  Hyodon  is  due  almost  entirely  to 


EVOLUTION    AND    SIGNIFICANCE    OF    CEREBRAL    CORTEX      303 

the  enlargement  of  the  centers  for  taste/  and  these  reflex  centers 
are  found  to  be  very  complex.  The  enormous  increase  in  the 
mass  and  complexity  of  arrangement  of  the  gustatory  neurons  in 
Carpiodes  does  not  imply  any  higher  organization  from  the 
standpoint  of  range  of  behavior  (see  p.  19)  than  in  Hyodon. 
The  apparatus  is  more  efficient  as  a  means  of  sorting  out  food 
particles  from  mud,  but  we  do  not  rank  this  form  of  activity 
very  high  in  our  scale  of  behavior. 


medulla 
oblongata- 


Fig.  136. — Illustrations  of  the  brains  of  two  rather  closely  allied  species 
of  fishes  showing  very  different  development  of  the  reflex  centers  of  the 
medulla  oblongata:  (1)  Hyodon  tergisus,  the  moon-eye,  (,2)  Carpiodes  tumi- 
dus,  a  carp-hke  species.     (After  C.  L.  Herrick.) 


In  general,  in  the  execution  of  a  complicated  reflex  many  inter- 
connected nerve-centers  are  so  arranged  that  they  discharge 
into  a  common  final  path  or  an  integrated  series  of  such  coordi- 
nated paths.  The  movements  involved  in  the  act,  if  performed 
at  all,  must  follow  in  a  definite  sequence  which  is  structurally 

^  For  an  analysis  of  this  gustatory  apparatus  in  fishes,  see  Herrick,  C. 
JuDSON.  The  Central  Gustatory  Paths  in  the  Brains  of  Bony  Fishes, 
Jour.  Comp.  Neurol.,  vol.  xv,  190.5,  pp.  375—456. 


304  INTRODUCTION  TO  NEUROLOGY 

predetermined  in  the  inborn  organization  of  the  nerve-centers 
concerned.  In  the  variable  type  of  response,  on  the  other  hand, 
the  association  centers  involved  are  so  arranged  that  many  final 
paths  leading  to  different  systems  of  coordinated  motor  centers 
diverge  from  a  single  center  of  correlation.  Which  of  these  paths 
will  be  taken  in  a  given  reaction,  that  is,  which  of  several  possible 
different  (or  even  antagonistic)  movements  will  result,  will  be 
determined  by  variable  physiological  factors  of  internal  resist- 
ance within  the  correlating  system  (fatigue,  habit,  the  influence 
of  memory  vestiges,  etc.);  accordingly,  the  response  is  not  pre- 
determined by  the  inborn  organization  of  the  apparatus. 

Definite,  well-established  reflexes  generally  follow  distinct 
nervous  pathways  between  sharply  limited  nerve-centers.  Be- 
tween these  centers  there  is  usually  found,  in  addition  to  the 
well  insulated  tracts  just  mentioned,  a  more  diffuse  and  loosely 
organized  entanglement  of  nerve-cells  and  fibers,  through  which 
nervous  impulses  may  be  more  slowly  transmitted  in  any  direc- 
tion. Tissue  of  this  character  is  found  throughout  the  entire 
length  of  the  central  nervous  system,  and  in  some  places  it  occu- 
pies extensive  regions  (especially  in  the  medulla  oblongata  and 
upper  part  of  the  spinal  cord)  which  are  termed  the  reticular  for- 
mation (see  pp.  65,  127,  158). 

The  reticular  formation  is  the  parent  tissue  out  of  which  the 
higher  correlation  centers  have  been  differentiated.  In  the 
spinal  cord  and  medulla  oblongata,  where  its  character  is  most 
clearly  seen,  it  receives  fibers  from  all  of  the  sensory  centers 
and  may  discharge  motor  impulses  into  efferent  centers  of  con- 
tiguous or  very  remote  regions.  In  the  higher  parts  of  the  brain 
the  elaborate  association  centers  of  the  thalamus  and  cerebral 
hemispheres  have  been  developed  from  such  a  primitive  matrix, 
and  these  centers  are  interconnected  by  similar  undifferentiated 
nervous  tissue. 

The  details  of  the  functional  connections  of  the  reflex  centers 
of  the  brain  stem  are  much  more  precisely  known  than  are  those 
of  the  higher  correlation  centers  of  the  thalamus  and  cerebral 
cortex.  And,  in  fact,  it  is  essential  that  these  details  be  fairly 
well  understood  before  the  functions  of  the  higher  centers  can 
be  investigated;  for  all  nervous  impulses  which  reach  these  higher 
centers  must  first  pass  through  the  lower  centers  and  there  be 


EVOLUTION    AND    SIGNIFICANCE    OF    CEREBRAL    CORTEX      305 

combined  into  reflex  systems  or  otherwise  correlated.  The 
afferent  stimuh  which  reach  the  cerebral  cortex  are  not  crude 
sensory  impressions,  but  purposeful  reflex  combinations,  often 
including  sensory  data  from  several  different  sense  organs. 

The  nerve-centers  of  the  spinal  cord  and  brain  stem  in  general 
are  of  this  more  rigid  type,  the  internal  adjustments  of  the  sys- 
tem being,  for  the  most  part,  as  mechanically  determined  as  are 
those  of  an  automatic  telephone  exchange.  The  cerebellum  is 
the  highest  member  of  this  series,  exerting  a  regulatory  and  re- 
inforcing influence  upon  all  of  the  other  members.  Nevertheless 
the  cerebellum  adds  no  new  types  of  reaction  or  combinations  of 
reactions  to  those  of  the  brain  stem;  its  cortex  shows  little  de- 
monstrable localization  of  different  functions,  and  its  efferent 
tracts  are  physiologically  related  to  a  hmited  number  of  pre- 
established  systems  of  motor  coordination  in  the  brain  stem  and 
spinal  cord.  In  all  of  these  respects  the  contrast  between  the 
cerebellar  cortex  and  the  cerebral  cortex  is  very  striking. 

The  variable  or  individually  modifiable  type  of  reaction  is 
served  chiefly  by  the  cerebral  cortex  and  its  immediate  depend- 
encies, though  some  capacity  of  this  sort  is  found  in  the  brain 
stem,  as  shown  by  the  behavior  of  lower  vertebrates  which  lack 
the  cerebral  cortex.  This  type  of  reaction  is  geneticallj^  related 
with  that  modifiability  arising  from  variable  internal  physio- 
logical states  which  we  have  mentioned  as  present  in  the  reflex 
centers.  There  is  no  proof  that  the  simpler  forms  of  this  indi- 
vidually modifiable  behavior  are  conscious,  though  the  higher 
forms  are  certainly  so. 

The  cerebral  cortex  can  in  no  case  act  independently  of  the 
reflex  centers  of  the  brain  stem,  but  always  through  the  agency 
of  these  centers.  It  is  superposed  upon  them  much  as  the  cere- 
bellum is,  though  the  control  exerted  is  of  a  very  different  tj^pe. 
Here  there  is  a  very  elaborate  regional  differentiation  of  the 
cortex  with  an  infinite  complexity  of  associational  connections. 
The  efferent  pathways,  moreover,  are  not  phj^siologically  homo- 
geneous; but  they  are  so  diversified  that  any  possible  combina- 
tion of  the  organs  of  response  may  be  effected  by  associations 
within  the  cortex.  The  various  afferent  functional  sj^stems  enter 
sharply  circumscribed  cortical  areas  (the  sensory  projection 
centers);  and  the  efferent  fibers  likewise  leave  the  cortex  from 
20 


306  INTRODUCTION  TO   NEUROLOGY 

functionally  defined  motor  areas,  each  group  of  muscles  which 
cooperate  in  definite  reaction  complexes  (termed  synergic 
muscles,  see  p.  35)  being  excited  from  a  definite  part  of  the  motor 
cortical  field,  whose  motor  tract  is  anatomically  distinct  through- 
out its  entire  further  course  from  the  cortex  to  the  periphery. 
Between  the  sensory  projection  centers  and  the  motor  areas  are 
interpolated  the  association  centers,  and  these  are  so  arranged 
that  all  correlation,  integration,  and  assimilation  of  present 
sensory  impulses  with  memory  vestiges  of  past  reactions  are 
completed,  and  the  nature  of  the  response  to  be  made  is  deter- 
mined before  the  resultant  nervous  impulses  are  discharged  into 
the  motor  centers.  Only  such  of  the  motor  areas  will  be  excited 
to  function  as  are  necessary  for  evoking  the  particular  reaction 
which  is  the  appropriate  (that  is,  adaptive)  response  to  the  total 
situation  in  which  the  body  finds  itself.  This  arrangement  of 
association  centers  in  relation  to  a  series  of  distinct  motor  areas 
provides  the  flexibility  necessary  for  complex  delayed  reactions 
whose  character  is  not  predetermined  by  the  nature  of  the  con- 
genital pattern  of  the  nervous  connections.^ 

The  thalamus,  as  we  have  seen  (p.  163),  has  its  own  intrinsic  system 
of  association  centers  which  discharge  downward  into  the  cerebral  pedun- 
cles, and  this  is  the  primary  reflex  apparatus  of  this  part  of  the  brain  The 
thalamo-cortical  connections  arose  to  prominence  later  in  the  evolutionary 
history,  though  feeble  rudiments  of  these  are  present  in  lower  brains. 
Parallel  with  the  enlargement  of  these  cortical  connections  a  special  part  of 
the  thalamus  was  set  apart  for  them,  and  from  the  Amphibia  upward  in  the 
animal  scale  this  dorsal  part  of  the  thalamus  assumed  increasingly  greater 
importance.  This  part  is  termed  by  Edinger  the  neothalamus,  and  makes 
up  by  far  the  larger  part  of  the  thalamus  in  the  human  and  all  other  mam- 
maUan  brains.  It  occupies  the  dorso-lateral  part  of  the  thalamus  proper  and 
comprises  most  of  the  great  thalamic  nuclei  (lateral  and  ventral  nuclei, 
pulvinar  and  lateral  and  medial  geniculate  bodies).  The  primitive  in- 
trinsic reflex  thalamic  apparatus  in  man  is  a  relatively  unimportant  area 
of  medial  gray  matter  and  the  subthalamic  region  (corpus  Luysii,  lattice 
nucleus,  etc.,  not  to  be  confused  with  the  hypothalamus  which  hes  farther 
down  in  the  tuber  cinereum  and  mammillary  bodies). 

The  neothalamus,  accordingly,  serves  as  a  sort  of  vestibule  to  the  cortex, 
every  afferent  impulse  from  the  sensory  centers  (except  the  olfactory  sys- 
tem) being  here  interrupted  by  a  synapse  and  opportunity  offered  for  a  wide 
range  of  subcortical  associations.  The  olfactory  cortex  (hippocampal  for- 
mation) has  a  similar  relation  to  subcortical  correlation  centers  in  the  olfac- 
tory area  in  the  anterior  perforated  space,  septum,  etc. 

ijThe  paragraphs  which  follow  (pp.  306-311)  are  reproduced  with  slight 
modification  from  The  Journal  of  Animal  Behavior,  vol.  iii,  1913,  pp.  228- 
236. 


EVOLUTION    AND    SIGNIFICANCE    OF    CEREBRAL    CORTEX      307 

From  these  anatomical  considerations  it  follows  that  no  simple  sensory 
impulse  can,  under  ordinary  circumstances,  reach  the  cerebral  cortex 
without  first  being  influenced  by  subcortical  correlation  centers,  within 
which  complex  reflex  combinations  may  be  effected  and  various  automatisms 
set  off  in  accordance  with  their  preformed  structure.  These  subcortical 
systems  are  to  some  extent  modifiable  by  racial  and  individual  experience, 
but  their  reactions  are  chiefly  of  the  invariable  or  stereotyjDed  character, 
with  a  relatively  hmited  range  of  possible  reaction  types  for  any  given 
stimulus  complex. 

It  is  shown  by  the  lower  vertebrates  which  lack  the  cerebral  cortex  that 
these  subcortical  mechanisms  are  adequate  for  all  of  the  ordinary  simple 
processes  of  hfe,  including  some  degree  of  associative  memory.  But  here, 
when  emergencies  arise  which  involve  situations  too  complex  to  be  resolved 
by  these  mechanisms,  the  animal  will  pay  the  inevitable  penalty  of  failure — ■ 
perhaps  the  loss  of  his  dinner,  or  even  of  his  life. 

In  the  higher  mammals  with  well-developed  cortex  the  automatisms  and 
simple  associations  are  hkewise  performed  in  the  main  by  the  subcortical 
apparatus,  but  the  inadequacy  of  this  apparatus  in  any  particular  situation 
presents  not  the  certainty  of  failure,  but  rather  a  dilemma.  The  rapid 
preformed  reflex  mechanisms  fail  to  give  relief,  or  perhaps  the  situation  pre- 
sents so  many  complex  sensory  excitations  as  to  cause  mutual  interference 
and  inhibition  of  all  reaction.  There  is  a  stasis  in  the  subcortical  centers. 
Meanwhile  the  higher  neural  resistance  of  the  cortical  pathways  has  been 
overcome  by  summation  of  stimuh  and  the  cortex  is  excited  to  function. 
Here  is  a  mechanism  adapted,  not  for  a  limited  number  of  predetermined 
and  immediate  responses,  but  for  a  much  greater  range  of  combination  of 
the  afferent  impressions  with  each  other  and  with  memory  vestiges  of  pre- 
vious reactions  and  a  much  larger  range  of  possible  modes  of  response  to  any 
given  set  of  afferent  impressions.  By  a  process  of  trial  and  error,  perhaps, 
the  elements  necessary  to  effect  the  adaptive  response  may  be  assembled 
and  the  problem  solved. 

It  is  evident  here  that  the  physiological  factors  in  the  dilemma  or  problem 
as  this  is  presented  to  the  cortex  are  by  no  means  simple  sensory  impres- 
sions, but  definitely  organized  systems  of  neural  discharge,  each  of  which  is  a 
physiological  resultant  of  the  reflexes,  automatisms,  impulses,  and  inhibi- 
tions characteristic  of  its  appropriate  subcortical  centers.  The  precise  form 
which  these  subcortical  combinations  will  assume  in  response  to  any  par- 
ticular excitation  is  in  large  measure  determined  by  the  structural  connec- 
tions of  these  centers  inter  se.  And  the  pattern  of  these  connections  is 
tolerably  uniform  for  aU  members  of  any  animal  race  or  species.  This 
implies  that  it  is  hereditary  and  innate.  This  is  the  underlying  basis  of 
instinct. 

The  connections  between  the  cortical  centers,  on  the  other  hand,  are 
much  less  definitely  laid  dowTi  in  the  hereditary  pattern.  The  details  of 
the  definitive  association  pattern  of  any  individual  are  to  a  greater  degree 
fixed  by  his  particular  experience.  This  is  the  basis  of  docihty  and  the 
individuaUy  modifiable  or  inteUigent  types  of  behavior.  The  tj^pical  cor- 
tical activities,  even  when  physiologically  considered,  are  far  removed  indeed 
from  those  of  the  brain  stem. 

It  should  be  emphasized,  however,  that  the  differences  between  the  cor- 
tex and  the  lower  centers  of  the  brain  stem,  so  far  as  these  can  be  deduced 
from  a  study  of  structure  and  from  physiological  experiment,  are  relative  and 
not  absolute.    Indeed,  the  general  pattern  of  the  regional  locaUzation  of  the 


308  INTRODUCTION  TO  NEUROLOGY 

cortex  itself  is  innate,  and  in  adult  life  the  cortex  has  acquired  many  more 
characteristics  similar  to  those  of  the  brain  stem,  with  its  own  systems  of 
acquired  automatisms  and  habitually  fixed  types  of  response.  The  larger 
association  centers  retain  their  plasticity  longest,  but  ultimately  these  also 
cease  to  exhibit  new  types  of  correlation,  and  this  marks  the  onset  of 
senihty. 

The  relations  of  the  cerebral  cortex  to  the  cerebellar  cortex  and  the 
brain  stem  have  been  compared  (p.  192)  to  those  of  an  enlarged  judicial 
branch  of  the  central  government  charged  with  the  duty  of  interpreting  the 
decrees  of  the  lower  legislative  centers  and  dominating  the  administrative 
machinery,  and  with  the  additional  power  of  shaping  the  general  policy  of 
the  government. 

Dewey's  stimulating  analysis^  of  the  reflex  arc  concept  or,  as  he  prefers 
to  say,  the  organic  circuit  concept  implies  that  the  synthesis  of  the  elements 
of  a  complex  chain  reflex  into  an  organic  unity  is  the  essential  prerequisite 
of  that  apperceptive  process  which  will  make  the  total  experience  of  value 
for  futm'e  discriminative  responses — for  learning  by  experience.  This, 
which  is  true  in  the  individual  learning  process,  is  also  true  phylogenetically. 
The  correlation  centers  (and  then-  capacity  for  the  preservation  of  vestiges 
of  past  reactions)  are  the  organic  mechanism  for  this  synthesis.  They  make 
it  possible  that  a  new  stimulus  may  be  reacted  to,  not  as  a  detached  element, 
but  as  a  component  of  a  complex  series  of  past  and  present  adjustments,  to 
which  it  is  assimilated  in  the  association  centers — apperception.  This 
assimilation  or  apperceptive  process  is  an  integral  part  of  the  receptor  proc- 
ess in  the  higher  centers,  giving  the  quale  to  the  idea  of  the  exciting  object. 
Cotemporaneously  with  this  stimulus-apperception  process  we  have  an 
apperception-response-activity  giving  the  object-  or  purpose-idea,  so  that 
the  entire  reaction  is  to  be  regarded  as  stimulus-apperception-response,  as  a 
functional  unity  rather  than  as  a  sequence:  stimulus>apperception>re- 
sponse. 

Dewey's  organic  circuit  concept  is  elaborated  in  terms  of  psychology. 
Let  us  see  how  it  may  be  applied  to  biological  behavior. 

The  simple  reflex  is  commonly  regarded  as  a  causal  sequence :  given  the 
gun  (a  physiologically  adaptive  structure),  load  the  gun  (the  constructive 
metabolic  process),  aim,  pull  the  trigger  (application  of  the  stimulus),  dis- 
charge the  projectile  (physiological  response),  hit  the  mark  (satisfaction  of 
the  organic  need) .  All  of  the  factors  may  be  related  as  members  of  a  simple 
mechanical  causal  sequence  except  the  aim.  For  this  in  our  illustration 
a  glance  backward  is  necessary.  An  adaptive  simple  reflex  is  adaptive 
because  of  a  pre-established  series  of  functional  sequences  which  have  been 
biologically  determined  by  natural  selection  or  some  other  evolutionary 
process.  This  gives  the  reaction  a  definite  aim  or  objective  purpose.  In 
short,  the  aim,  like  the  gun,  is  provided  by  biological  evolution,  and  the 
whole  process  is  implicit  in  the  structure-function  organization  which  is 
characteristic  of  the  species  and  whose  nature  and  origin  we  need  not  here 
further  inquire  into. 

Now,  passing  to  the  more  complex  instinctive  reactions,  so  far  as  these 
are  unconscious  automatisms,  they  may  be  elaborations  of  chain  reflexes 
of  the  type  discussed  above  (p.  61).     But  the  aim  (biological  purpose)  is 

1  The  Reflex  Arc  Concept  in  Psychology,  Psych.  Rev.,  vol.  iii,  p.  357, 
1893.  See  also  Dewey's  later  statement  in  Jour.  Philos.,  Psych.,  and  Sci. 
Methods,  vol.  ix,  Nov.,  1912,  pp.  664-668,  especiaUy  thejootnote  on  p.  667, 


EVOLUTION    AND    SIGNIFICANCE    OF    CEREBRAL    CORTEX      309 

SO  inwTought  into  the  course  of  the  i)rocess  that  it  cannot  be  dissociated. 
Each  step  is  an  integral  part  of  a  unitary  adaptive  process  to  serve  a  definite 
biological  end,  and  the  animal's  motor  acts  are  not  satisfying  to  him  unless 
they  follow  this  predetermined  sequence,  though  he  himself  may  have  no 
clear  idea  of  the  aim. 

These  reactions  are  typical  organic  circuits.  The  cycle  in  some  of  the 
instincts  of  the  deferred  type  comprises  the  whole  life  of  the  individual. 
In  other  cases  the  cycle  is  annual  (as  in  bird  migrations,  etc.),  diurnal,  or 
linked  up  with  definite  physiological  rhythms  (e.  g.,  the  nidification  of  birds 
as  described  by  F.  H.  Herrick,  see  p.  61).  In  still  other  cases  there  is  no 
apparent  simple  rhythm.  But  always  the  process  is  not  a  simple  sequence 
of  distinct  elements,  but  rather  a  series  of  reactions,  each  of  which  is  .shaped 
by  the  interactions  of  external  stimuli  and  a  preformed  or  innate  structure 
which  has  been  adapted  by  biological  factors  to  modify  the  response  to  the 
stimuU  in  accordance  with  a  purpose,  which  from  the  standpoint  of  an  out- 
side observer  is  teleological,  i.  e.,  adapted  to  conserve  the  welfare  of  the 
species. 

Every  intelligently  directed  response  to  external  stimulation  involves  a 
large  measure  of  highly  complex  unconscious  cerebration  of  this  type; 
and  it  is  possible  to  describe  with  considerable  precision  the  mechanisms  of 
the  subcortical  activities  involved  in  many  of  those  organic  circuits  which 
are  commonly  regarded  as  tj^pically  cortical. 

Much  of  that  which  goes  in  psychological  literatm-e  under  such  contra- 
dictory terms  as  unconscious  mind  or  subconscious  mind  is,  in  reality,  the 
subcortical  elaboration  of  types  of  action  system  which  ordinarily  do  not 
involve  the  cortex  at  all,  but  which  upon  occasion  may  be  linked  up  with 
cortical  associational  processes  and  then  come  into  consciousness  in  such  a 
form  as  to  suggest  to  introspection  that  they  are  all  of  a  piece  with  the 
conscious  process  with  which  they  are  related.  In  fact,  within  the  cortex 
itself  there  are  doubtless  many  routine  activities  which  do  not  ordinarily 
come  into  consciousness,  particularly  of  the  sort  known  as  acquu-ed  autom- 
atisms or  lapsed  intelligence;  and  these,  though  of  quite  different  origin 
from  the  innate  instinctive  systems,  cannot  easily  be  distinguished  from 
them  in  the  form  in  which  they  are  experienced  in  the  adult. 

In  the  organic  circuit  as  defined  by  Dewey  the  process  is  considered  as  a 
whole,  so  that  the  response  is  conceived  as  logically  imphcit  in  the  stimulus. 
The  motor  reaction,  he  says,  is  not  merely  to  the  stimulus;  it  is  into  the 
stimulus.  "It  occurs  to  change  the  sound,  to  get  rid  of  it.  What  we 
have  is  a  circuit,  not  an  arc,  or  broken  segment  of  a  circle.  This  circuit  is 
more  truly  termed  organic  than  reflex,  because  the  motor  response  deter- 
mines the  stimulus  just  as  truly  as  sensory  stimulus  determines  movement." 
This  notion,  which  is  difficult  for  the  practical  scientific  mind  to  understand, 
is  considerably  clarified  by  some  neurological  considerations. 

From  the  standpoint  of  the  cerebral  cortex  considered  as  an  essential 
part  of  the  mechanism  of  higher  conscious  acts,  every  afferent  stimulus,  as 
w^e  have  seen,  is  to  some  extent  affected  by  its  passage  through  various  sub- 
cortical correlation  centers  (i.  c,  it  carries  a  quale  of  central  origin).  But 
this  same  afferent  impulse  in  its  passage  through  the  spinal  cord  and  brain 
stem  may,  before  reaching  the  cortex,  discharge  collateral  impulses  into  the 
lower  centers  of  reflex  coordination,  from  which  incipient  (or  even  actually 
consummated)  motor  responses  are  discharged  previous  to  the  cortical  reac- 
tion. These  motor  discharges  may,  through  the  "back  stroke''  action,  in 
tiu-n  exert  an  influence  upon  the  slower  cortical  reaction.     Thus  the  lower 


310 


INTRODUCTION  TO   NEUROLOGY 


reflex  response  may  in  a  literal  physiological  sense  act  into  the  cortical  stim- 
ulus complex  and  become  an  integral  part  of  it. 

But  there  is  another  aspect  of  the  problem  which  has  recently  been 
brought  to  our  notice  by  Kappers.^  It  is  a  well-known  fact,  which  is  not 
often  taken  account  of  in  this  connection,  that  the  descending  cortical 
paths  (pyramidal  tracts)  do  not  typically  end  directly  upon  the  peripheral 
motor  neurons  whose  functions  they  excite,  but  rather  upon  intercalary 
neurons  which  lie  in  the  reticular  formation  or  even  in  the  adjacent  sensory 


Fig.  137. — Diagram  of  the  relations  of  the  pyramidal  tract  in  a  rabbit  or 
similar  lower  mammalian  brain.  Sensory  stimuli  enter  the  spinal  cord  from 
the  skin  through  the  peripheral  sensory  neuron,  S,  and  ascend  to  the  cere- 
bral cortex  through  the  lemniscus,  L.  The  descending  pyramidal  tract, 
P,  lies  in  the  dorsal  funiculus  of  the  spinal  cord.  Its  intercalary  neuron,  I, 
may  be  stimulated  by  both  the  peripheral  neuron,  S,  and  by  the  pyramidal 
tract,  P.     It  discharges  upon  the  peripheral  motor  neuron,  M. 


centers.     These  intercalary  neurons,  in  turn,  excite  the  peripheral  motor 
neurons.     The  same  intercalary  neuron  which  receives  the  terminals  of  the 

1  Kappers,  C.  U.  Ariens.  Ueber  die  Bildung  von  Faserverbindungen  auf 
Grund  von  simultanen  und  sukzessiven  Reizen.  Bericht  iiber  den  III 
Kongress  fiir  experimentelle  Psychologie  in  Frankfurt  a.  Main,  1908.  Also 
Weitere  Mitteilungen  iiber  Neurobiotaxis.  FoHa  Neuro-Biologica,  Bd. 
I,  No.  4,  April,  1908,  pp.  507-532. 

See  also  Dearborn,  G.  V.  N.  Kinesthesia  and  the  Intelhgent  WUl, 
Amer.  Jour,  of  Psychol.,  vol.  xxiv,  1913,  pp.  204-255. 


EVOLUTION    AND    SIGNIFICANCE    OF    CEREBRAL    CORTEX      311 

pyramidal  tract  also  receives  collaterals  from  the  peripheral  sensory  neurons 
of  its  own  segment  (Fig.  137).  This  arrangement  is  the  explanation  of  the 
fact  that  the  pyramidal  tract  fibers  descend  through  the  human  spinal 
cord  for  the  most  part  in  the  dorso-lateral  region,  not  in  the  ventral  funic- 
ulus like  most  other  motor  tracts.  In  most  lower  mammals  the  pyramidal 
tract  actually  descends  within  the  dorsal  funiculus  in  the  closest  possible 
association  with  the  peripheral  sensory  fibers,  and  this  arrangement  is 
clearly  the  primitive  relation  of  the  descending  cortical  pathway. 

Accordingly,  stimulation  of  the  skin  of  the  body  excites  a  dorsal  spinal 
root  fiber  which  ascends  toward  the  cortex  within  the  spinal  cord  and  also 
gives  collateral  branches  to  intercalary  neurons  of  the  spinal  cord  itself. 
The  latter  neurons  may  excite  motor  elements  of  the  spinal  cord  to  an  im- 
metUate  reflex  response  which  is  well  under  way  before  the  cortical  return 
motor  impulse  gets  back  to  the  spinal  cord  and  discharges  into  these  same 
intercalary  neurons  which  are  already  under  sensory  stimulation  directly 
from  the  periphery.  The  effect  of  this  arrangement  is  that  the  central 
motor  path  during  function  is  under  the  influence  of  sensory  stimulation  at 
both  endSj  and  is  not,  as  commonly  described,  under  simple  sensory  stimula- 
tion at  the  cortical  end  and  purely  emissive  in  function  at  the  spinal  end. 

Viewed  from  the  standpoint  of  cerebral  dynamics,  the  exact  physiological 
effect  of  the  discharge  of  a  central  motor  bundle  such  as  the  pyramidal  tract 
will  be  dependent  upon  the  combined  action  of  the  sensory  stimulation  at 
the  cortical  end  and  the  state  of  sensory  excitation  at  the  spinal  end,  as  well 
as  upon  the  resistance  of  the  motor  apparatus  itself. 

We  saw  in  a  previous  paragraph  how  the  simple  reflexes  of  the  spinal 
cord  may  become  factors  in  the  stimulus  complex  of  the  cortex.  Here  we 
find,  conversely,  that  the  efferent  cortical  discharge  may  become  a  factor  in 
the  local  reflex  stimulation  of  a  motor  spinal  neuron.  From  both  stand- 
points Dewey's  conception  of  the  unitary  nature  of  the  organic  circuit,  as 
contrasted  with  the  classical  reflex  arc  concept,  receives  strong  support. 

The  thalamic  correlation  centers  probably  serve  as  the  organs  par  excel- 
lence where  are  elaborated  those  organic  circuits  which  give  to  the  higher 
apperceptive  processes  of  the  cortex  that  quale  to  which  Dewey  refers. 
The  origin  of  this  quale  is  to  be  sought  partly  in  the  subcortical  assimilation 
of  a  present  stimulus  complex  to  the  pre-existing  organic  circuits  structur- 
ally laid  down  in  the  reflex  mechanism,  and  partly  in  an  affective  quality 
pertaining  to  the  several  organic  circuits  involved  in  the  reaction.  This 
affective  quality  may  be  innate  or  it  may  have  been  acquired  by  experience 
of  the  results  of  previous  reactions  of  the  sort  in  question. 

Head  and  Holmes  have  brought  forward  some  very  interesting  evidence 
that  not  only  the  affective  quale  of  sensations  but  also  the  emotional  life 
in  general  is  functionally  related  to  the  primitive  intrinsic  nuclei  of  the 
thalamus,  rather  than  to  cortical  activity  (see  p.  253).  And  certainly 
there  is  much  evidence  in  the  behavior  of  lower  animals,  especially  birds, 
that  a  high  degree  of  emotional  activity  is  possible  where  the  basal  centers 
are  highly  elaborated  but  the  cerebral  cortex  is  small  and  very  simply  organ- 
ized. 

From  all  of  these  considerations  it  seems  probable  that  the  functions  of 
the  higher  association  centers  of  the  cerebral  cortex  do  not  consist  of  the 
elaboration  of  crude  sensory  data  or  of  any  similar  elements,  but  rather  of 
the  assembling  and  integration  of  highly  elaborated  subcortical  organic  cir- 
cuits which  in  the  aggregate  make  up  the  greater  part  of  the  reflex  and  in- 
stinctive life  of  the  species. 


312  INTRODUCTION  TO  NEUROLOGY 

The  normal  newborn  child  brings  into  the  world  an  inherited 
form  of  body  and  brain  and  a  complex  web  of  nerve-cells  and 
nerve-fibers  which  provide  a  fixed  mechanism,  common  except 
for  minor  variations  to  all  members  of  the  race  alike,  for  the 
performance  of  the  reflex  and  instinctive  actions.  The  pat- 
tern of  this  hereditary  fabric  can  be  changed  only  very  slowly 
by  the  agency  of  selective  matings  and  other  strictly  biological 
factors  or  by  degenerations  of  a  distinctly  pathological  sort.  It  is 
thus  manifest  that  the  improvement  of  the  racial  stock  of  normal 
individuals  by  the  practice  of  eugenics  must  necessarily  be  very 
slow,  though  the  improvement  of  defective  or  pathological  strains 
by  selective  matings  so  as  to  breed  out  the  objectionable  charac- 
teristics is  fortunately  in  most  cases  more  readily  accomplished. 

But  in  addition  to  this  hereditary  organization  the  newborn 
child  possesses  the  large  association  centers  of  the  brain  with 
their  vast  and  undetermined  potencies,  the  exact  form  of  whose 
internal  organization  is  not  wholly  laid  down  at  birth,  but  is 
in  part  shaped  by  each  individual  separately  during  the  course  of 
the  growth  period  by  the  processes  of  education  to  which  he  is 
subjected,  that  is,  by  his  experience.  This  capacity  for  indi- 
viduality in  development,  this  ability  to  profit  by  experience, 
this  docility,  is  man's  most  distinctive  and  valuable  character- 
istic. And  since  the  form  which  this  modifiable  tissue  will  take 
is  determined  by  the  environing  influences  to  which  "the  child 
is  subjected,  and  since  these' influences  are  largely  under  social 
control,  it  follows  that  human  culture  can  advance  by  leaps  and 
bounds  wherever  a  high  level  of  community  life  and  educational 
ideals  is  maintained. 

So  well  have  we  learned  the  lesson  that  the  child  brings  with 
him  into  the  world  no  mental  endowments  ready-made — no 
knowledge,  no  ideas,  no  morals — but  that  these  have  to  be 
developed  anew  in  each  generation  under  the  guiding  hand  of 
education,  that  we  devote  one-third  of  the  expected  span  of  life 
of  our  most  promising  youth  to  the  educational  training  neces- 
sary to  ensure  the  highest  possible  development  of  the  latent 
cultural  capacities  of  these  association  centers  of  the  cerebral 
cortex. 

But  we  have  often  been  blind  to  the  other  side  of  the  picture. 
We  have  seen  above  that  the  adult  cortex  cannot  function  save 


EVOLUTION    AND    SIGNIFICANCE    OF    CEREBRAL    CORTEX      313 

through  the  reflex  machinery  of  the  brain  stem,  and  it  must  not 
be  forgotten  in  our  pedagogy  that  this  relation  holds  in  a  much 
more  vital  and  significant  sense  in  the  formative  years  of  the 
child.  It  is  true  that  the  child  is  born  with  no  mental  endow- 
ments; but  how  rich  is  his  inheritance  in  other  respects!  He  has 
an  immense  capital  of  preformed  and  innate  ability  which  takes 
the  form  of  physiological  vigor  and  instinctive  and  impulsive 
actions,  performed  for  the  most  part  automatically  and  uncon- 
sciously. This  so-called  lower  or  animal  nature  is  ever  present 
with  us.  In  infancy  it  is  dominant;  childhood  is  a  period  of 
storm  and  stress,  seeking  an  equilibrium  between  the  stereotyped 
but  powerful  impulsive  forces  and  the  controls  of  the  nascent 
intellectual  and  moral  nature;  and  in  mature  years  one's  value  in 
his  social  community  life  is  measured  by  the  resultant  outcome  of 
this  great  struggle  in  childhood  and  adolescence.  This  struggle 
is  education. 

The  answer  to  the  riddle  of  life,  however,  lies  not  in  a  success- 
ful attack  upon  the  native  innate  endowments  of  the  child.  No, 
that  would  be  unbiological  and  wasteful,  for  our  world  of  ideas 
and  morals  is  no  artificial  world  within  the  cosmos,  but  it  is  a 
natural  growth,  which  is  as  truly  a  part  of  the  cosmic  process  as 
are  "ape  and  tiger  methods"  of  evolution.  No  higher  association 
center  of  the  human  brain  can  function  except  upon  materials  of 
experience  furnished  to  it  through  the  despised  lower  centers  of 
the  reflex  type.  So  also,  no  high  intellectual,  esthetic,  or  moral 
culture  can  be  reached  save  as  it  is  built  upon  the  foundation  of 
innate  capacities  and  impulses. 

We  are  gradually  learning  through  the  kindergarten  that  the 
most  economical  way  to  lead  a  child  into  the  realm  of  learning  is 
not  to  stamp  out  all  of  his  natural  interests  and  shut  him  up  with 
his  face  to  the  wall,  while  he  learns  by  rote  an  a-b-c  lesson  which 
is  neither  interesting  nor  useful.  On  the  contrary,  we  accept  as 
given  his  native  impulses  and  automatisms,  his  spontaneous 
interests  and  his  overproduction  of  useless  movements,  and  we 
use  these  as  the  capital  with  which  we  set  the  youngsters  up  in 
the  serious  business  of  the  acquisition  of  culture.  But  how  does 
it  happen  that  we  make  so  small  use  of  the  principles  here  learned 
in  the  later  years  of  the  child's  schooling? 

Not  all  of  the  instincts  with  which  man  is  by  nature  endowed 


314  INTEODUCTION  TO  NEUROLOGY 

come  into  function  in  a  sucking  babe  or  a  kindergarten  pupil. 
Childish  curiosity  is  our  strongest  ally,  if  only  we  can  use  it 
wisely,  throughout  the  whole  of  the  educational  career  from  in- 
fancy to  the  graduate  school.  Anger  is  a  mighty  passion  in  child- 
hood. It  is  not  wise  to  eradicate  it  altogether;  rather  keep  it, 
though  under  curb,  for  there  are  times  when  real  abuses  arise 
which  require  that  the  man  know  how  to  hit  and  to  hit  hard. 
And  so  with  the  instincts  of  self-preservation,  of  fear,  of  sex — 
these  all  have  their  parts  to  play  in  the  nobler  works  of  life  and 
are  by  no  means  to  be  eradicated.  The  ascetic  ideal  of  mortifica- 
tion of  the  flesh  as  a  means  of  grace  is  fundamentally  wrong  in 
principle.  Our  case  calls  for  no  blind,  indiscriminate  attack 
upon  the  world  and  the  flesh,  but  rather  the  subjugation  and  dis- 
cipline of  these,  so  that  we  may  use  them  effectively  in  our  attack 
upon  the  devil. 

Conflict  is  inherent  in  the  cosmic  process,  at  least  in  the  bio- 
logical realm,  from  beginning  to  end.  There  is  the  struggle  for 
physical  existence  among  the  animals.  And  even  in  the  lower 
ranks  of  life  there  arises  also  the  struggle  within  the  individual 
between  stereotyped  innate  tendencies  or  instincts  and  individu- 
ally acquired  experience.  This  is  clearly  shown  by  experiments 
on  animals  as  low  down  as  the  Protozoa.  And  out  of  this  inner 
conflict  or  dilemma  intelligence  was  born.  With  the  gradual 
emergence  of  self-consciousness  in  this  process  arises  the  eternal 
struggle  with  self,  that  conflict  which  leads  to  the  bitter  cry, 
"When  I  would  do  good  evil  is  present  with  me."  Conflict, 
then,  lies  at  the  basis  of  all  evolution,  and  the  factors  of  social 
and  even  of  moral  evolution  can  be  traced  downward  throughout 
the  cosmic  process. 

The  social  and  ethical  standards,  therefore,  have  not  arisen 
in  opposition  to  the  evolutionary  process  as  seen  in  the  brute 
creation,  but  within  that  process.  And  our  immediate  educa- 
tional problem  is  the  elaboration  of  a  practicable  system  of  pub- 
lic instruction  which  can  use  to  the  full  the  enormous  dynamic 
energy  in  the  hereditary  impulsive  and  instinctive  endowment  of 
the  child,  and  build  upon  this,  in  the  form  best  suited  to  the  re- 
spective capacities  of  all  the  separate  individuals,  a  properly 
ordered  sequence  of  studies  which  will  develop  the  latent  capac- 
ities of  each  pupil  and  ensure  a  vital  balance  between  the  strong 


EVOLUTION    AND    SIGNIFICANCE    OF    CEREBRAL    CORTEX      315 

blind  impulse  of  the  innate  nature  and  the  acquired  intellectual, 
esthetic,  and  moral  control. 

And  herein  lies  the  solution  of  the  problem  of  human  freedom, 
so  far  as  this  rests  within  our  own  control.  The  limits  of  one's 
powers  and  the  range  within  which  his  freedom  of  action  is  cir- 
cumscribed are  in  part  determined  by  his  hereditary  endowments 
and  by  environmental  influences  over  which  he  has  no  control. 
These  are  decreed  to  him  by  his  fate,  and  the  innate  organization 
of  the  nervous  system  is  the  chief  instrument  of  this  fate.  But 
man  differs  from  the  brute  creation  chiefly  in  that  he  can  more 
completely  control  his  own  environment  and  thereby  to  that 
extent  take  his  fate  into  his  own  hands;  in  other  words,  he  can 
enrich  his  own  experience  along  lines  of  his  own  selection.  To 
some  extent  each  individual  can  do  this  for  himself  through  self- 
culture;  but  to  ensure  the  best  results  of  such  efforts  there  must 
be  a  social  control  of  the  environment  as  a  whole  by  concerted 
community  action.  Individual  freedom  of  action  can,  therefore, 
attain  its  highest  efficiency  only  through  a  certain  amount  of 
voluntary  renunciation  of  the  selfish  interests  where  these  con- 
flict with  community  welfare.  Ethical  ideals  and  altruism  are 
as  truly  evolutionary  factors  in  human  societies  as  are  the  ele- 
mental laws  of  self-preservation  and  propagation  of  the  species.^ 

To  return  now  to  the  developing  nervous  system,  we  note  that 
the  educational  period  is  limited  to  the  age  during  which  the 
association  centers,  whose  form  is  not  predetermined  in  heredity, 
remain  plastic  and  capable  of  modification  under  environmental 
influence.  Ultimately  even  the  cerebral  cortex  matures  and 
loses  its  power  of  reacting  except  in  fixed  modes.  Its  unspecial- 
ized  tissue — originally  a  diffuse  and  equipotential  nervous  mesh- 
work— becomes  differentiated  along  definite  lines  and  the  funda- 
mental pattern  becomes  more  or  less  rigid.  The  docile  period  is 
past,  and  though  the  man  may  continue  to  improve  in  the 
technic  of  his  performance,  he  can  no  longer  do  creative  work. 
He  is  apt  to  say,  "The  dog  is  too  old  to  learn  new  tricks." 

^  In  tliis  connection  reference  may  be  made  to  two  very  interesting  ad- 
dresses recently  delivered  before  the  American  Society  of  Naturalists: 

Jennings,  H.  S.  1911.  Heredity  and  Personalitv,  Science,  N.  S.,  vol. 
xxxiv,  pp.  902-910. 

CoNKLiN,  EDwaN  G.  1913.  Heredity  and  Responsibility,  Science,  N.  S., 
vol.  xxxvii,  pp.  46-54. 


316  INTRODUCTION  TO   NEUROLOGY 

Whether  this  process  occurs  at  the  age  of  twenty  or  eighty  years, 
it  is  the  beginning  of  senility.  And,  alas,  that  this  coagulation 
of  the  mental  powers  often  takes  place  so  early!  Many  a  boy's 
brains  are  curdled  and  squeezed  into  traditional  artificial  molds 
before  he  leaves  the  grades  at  school.  His  education  is  complete 
and  senile  sclerosis  of  the  mind  has  begun  by  the  time  he  has 
learned  his  trade.  For  how  many  such  disasters  our  brick-yard 
methods  in  the  public  schools  are  responsible  is  a  question  of 
lively  interest. 

We  who  seek  to  enter  into  the  kingdom  of  knowledge  and  to 
continue  to  advance  therein  must  not  only  become  as  little 
children,  but  we  must  learn  to  continue  so.  The  problem  of 
scientific  pedagogy,  then,  is  essentially  this :  to  prolong  the  plas- 
ticity of  childhood,  or  otherwise  expressed,  to  reduce  the  in- 
terval between  the  first  childhood  and  the  second  childhood  to 
as  small  dimensions  as  possible. 


INDEX  AND  GLOSSARY 


The  references  are,  in  all  cases,  to  pages.  Numbers  referring  to  pages  upon  which  the 
item  is  figured  are  printed  in  black-faced  type.  Authors'  names  are  printed  in  small 
CAPITALS.  Brief  definitions  of  some  of  the  more  commonly  used  technical  terms  are  in- 
cluded in  this  Index;  for  fuller  de.-icriptions  consult  the  pages  cited.  Terms  which  are 
defined  in  this  Glossary  are  printed  in  black-faced  type.  The  names  of  fiber  tracts,  in 
general,  define  their  connections,  the  first  part  of  the  compound  word  indicating  the 
nucleus  of  origin  and  the  last  part  the  terminal  nucleus  (see  page  128).  To  facilitate 
cross-reference,  the  key-word  of  a  polj'noniial  term  is  capitalized  wherever  it  occurs  in  this 
Index  and  Glossary. 


Accommodation  of  vision,  143,  207, 
211,  232,  23-4,  2-47 

Acids,  sensitiveness  to,  72,  91,  242 

Acipenser  rubicundus,  nervous  sys- 
tem of,  151,  152 

Acoustic  apparatus.  See  Auditory 
apparatus. 

Acoustico-lateral  apparatus,  the  ner- 
vous mechanisms  of  the  internal 
ear  and  lateral  hne  organs  in  fishes 
and  amphibians.  See  Nerves, 
lateral,  and  Organs,  lateral  line. 

Action.     See  Behavior  and  Reflex. 

Action  system,  21,  32,  66 

Adi'enalin  (epinephrin),  231,  255,  256 

Affection,  affective  experience,  affec- 
tive tone,  pleasm-e-pain,  emotions, 
and  aUied  phenomena;  cf.  Feeling 
tone  and  Pain,  89,  167,  241,  249- 
262,  311 

Affective  tone.  See  Feeling  tone 
and  Affection. 

Afferent,  conducting  toward  a  cen- 
ter, 25,  42,  108,  126,  137,  145-150 

Agraphia,  loss  of  the  power  to  "UTite 

•    correctly,  292 

Agreeable  and  disagreeable.  See 
Affection. 

Ala  cinerea  (vagal  eminence,  emi- 
nentia  vagi,  trigonimi  vagi),  an 
eminence  in  the  floor  of  the  fourth 
ventricle  formed  by  the  dorsal 
Nucleus  of  the  vagus,  154,  156, 
164,  234,  244 

Alcohol,  sensitiveness  to,  242 

Alexia,  loss  of  the  power  of  reading 
(word -blindness),  292 

Altruism,  315 


Alveus,  association-fibers  which  con- 
nect the  Hippocampus  with  the 
Gyrus  hippocampi,  221,  222 

Ameboid,  resembling  an  ameba; 
apphed  to  the  supposed  outward 
and  inward  movement  of  proc- 
esses of  cells  dtu'ing  nervous  func- 
tion, 104 

Ameim-us  melas,  gustatory  nerves 
of,  245,  246 

Amnion's  horn.     See  Hippocampus. 

Amphibia,  nervous  system  of,  182, 
264 

Ampulla,  of  semicircular  canal,  183, 
196 

Amygdala.     See  Nucleus  amygdalae. 

Anatomy  of  nervous  system,  gen- 
eral, 106 

Andre-Thomas,  193 

Anger.  See  also  Affection,  89,  255, 
256,  314 

Anguis  fragihs,  parietal  eye  of,  212 

Animals,  contrasted  with  plants, 
22 

Anterior,  as  used  in  this  work, 
means  toward  the  head  end  of 
the  body;  as  used  in  the  B.  N.  A. 
tables  it  means  toward  the  ventral 
side,  115,  116 

Apathy,  S.,  55 

Apes,  nervous  S3'stem  of,  282,  286, 
290,  295 

Aphasia,  a  speech  defect  due  to  a 
cortical  injiuy,  or  more  broadly  any 
defect  in  symbolizing  relations;  cf. 
Speech,  apparatus  of,  291-293 

Aphemia,  loss  of  the  power  to  utter 
words,  292 

317 


318 


INDEX    AND    GLOSSARY 


Apoplexy,  293 
Apperception,  249,  296,  308 
Appetite,  240 

Aqueduct  of  Sylvius  (iter,  optocoele, 
mesocoele),    the   ventricle   of   the 
midbrain,  62,  121,  158,  160,  161 
Arachnoid,  the  middle  brain  mem- 
brane, 38 
Arbor    vitae,    the    tree-hke    appear- 
ance of  the  white  matter  of  the 
cerebellum  in  section,  190 
Archipallium,  the  olfactory  cerebral 
cortex,  including  the  Hippocam- 
pus  and    the    Gyrus   hippocampi 
(in  part),  217,  221,  222,  273,  284, 
288,  306 
Area,  acoustic.     See  Area,  acoustico- 
lateral.  Nucleus,  cochlear,  and 
Nucleus,  vestibular, 
acoustico-lateral  (in  fishes  =  tuber- 
culum    acusticum).     111,     112, 
123,  143,  149,  152,  187,  200 
cortical,  as  used  in  this  Index  is 
a  part  of  the   cerebral   cortex 
which  can  be  differentiated  from 
its  neighbors  structurally  by  the 
arrangement    of    its    cells    and 
fibers  (sometimes  termed  field) ; 
cf.    Center,    cortical,  273,    277, 
287,  288 
cutaneous,  111,  112,  123,  157 
general  somatic  sensory.  See  Area, 

cutaneous. 
olfactoria,   the  region   containing 
the  secondary  olfactory  centers, 
divided   into   anterior,    medial, 
intermediate  and  lateral  olfac- 
tory Nuclei,  165,  167,  215,  217, 
218,  219,  221,  306 
parolfactoria  of  Broca   (gyrus  ol- 
factorius  medialis  of  Retzius), 
a  portion  of  the  medial  Area  ol- 
factoria immediately  in  front  of 
the  Gyrus  subcallosus,  119 
perforata.      See    Substantia    per- 
forata, 
somatic,  a  small  region  in  the  fish 
brain  from  which  the  Neopal- 
lium and  Corpus  striatum  were 
developed.  111,  112,  123 
striata,  that  part  of  the  occipital 
lobe  of  the  cerebral  cortex  con- 
taining the  Line  of  Gennari ;  the 
visual  center,  268,  284 


Area,  visceral.  See  also  Lobe,  vis- 
ceral, HI,  112,  123,  148,  149,  152, 
153,  157,  237,  239,  240,  246,  303. 

Arteries,  nerves  of.  See  Vasomotor 
apparatus. 

Articulates,  behavior  of,  33 

Association,  correlation  involving  a 
high  degree  of  modifiability  and 
also  consciousness,  35,  64,  104, 
242,  258,  279,  290,  292,  295,  296, 
307 

Association    center.       See    Center, 
association, 
fibers.    See  Fiber,  association,  and 

Tract,  association, 
of  ideas,  295 
pattern,  291 
time  of,  98 

Asthma,  238 

Ataxia,  loss  of  the  power  of  muscular 
coordination,  137,  138 

Atropin,  231 

Attention,  103,  104 

Auditory  apparatus,  60,  62,  63,  70, 
85,  145,  147,  150,  157,  160,  163- 
167,  170,  195-203 

Auditory  reaction  time,  98 

AuERBACH,  plexus  of  (myenteric 
plexus),  241 

Aula,  the  anterior  end  of  the  third 
ventricle  where  it  communicates 
with  the  lateral  ventricles  by  way 
of  the  interventricular  Foramina. 

Auricle,  of  external  ear,  195 

Automatisms,  acquired,  35,  57,  286, 
301,  309 

Avalanche  conduction.  See  Conduc- 
tion, avalanche. 

Axis-cylinder,  the  central  protoplas- 
mic strand  of  a  nerve-fiber;  part 
of  the  Axon,  39 

Axon  (axis-cylinder  process,  neurite, 
neuraxon,  neuraxis),  a  process  of 
a  Neuron  which  conducts  impulses 
away  from  the  cell  body,  39,  40, 
44,  45,  47 

Axon  hillock,  the  point  of  origin  of  an 
axon  from  the  cell  body,  40,  41, 46 

Axone.     See  Axon. 


Back-stroke,  the  influence  which  a 
peripheral  organ  of  response  exerts 
back  upon  the  center  from  which 


INDEX    AND    GLOSSARY 


319 


the  response  was  excited ;  a  form  of 
chain  Reflex;   cf.   Reflex  circuit, 
260,  309 
Baillarger,  layer  of,  stripe  of.    See 

Line  of  Baillarger. 
Barker,  L.  F.,  36,  40,  49,  55,  94, 

124,  142,  159,  223 
Bartlemez,  G.  W.,  54,  181 
Basis     pedunculi     (pes     pedunculi, 
crusta),   the  ventral  part  of  the 
cerebral    Peduncle,   composed   of 
descending  fiber  tracts,  114 
Basle  nomina  anatomica  (B.  N.  A.), 

115,  116,  121,  122 
Bechterew,  W.,  159,  213,  299 
Bechterew,  vestibular  nucleus  of, 

184,  185 
Behavior,  invariable,  activities  whose 
character  is  determined  by  in- 
nate structure,  typified  by  reflex 
and  instinctive  actions,  31,  67, 
78,  115,  181,  363,  294,  301-304, 
312 
range  of,  19,  303 

variable,  activities  which  are  modi- 
fiable by  individual  experience, 
with  or  without  consciousness, 
31,  64,  67,  78,  101,  115,  181,  263, 
290,  294,  301-304,  312,  315,  316 
Bethe,  a.,  47,  55,  90 
Betweenbrain.    See  Diencephalon. 
Betz,  cells  of.    See  Cells  of  Betz. 
BiANCHi,  A.,  193 
Birds,  behavior  of,  61,  309,  311 

nervous  system  of,  187,  216 
Bladder,   innervation  of,   226,   232, 

243 
Blood,  coagulation  of,  255 
Blood-pressure,  104,  235 
Blood-vessels,  nerves  of.     See  Cir- 
culation  of   blood,   apparatus  of, 
and  Vasomotor  apparatus. 
B.  N.  A.     See  Basle  nomina  ana- 
tomica. 
Body  of  cell.    See  Cell  body. 

chromophilic.       See      Substance, 

chromophilic. 
of  fornix.  See  Fornix  body, 
geniculate,  lateral  (corpus  genicu- 
latum  laterale,  external  gen- 
iculate body),  a  visual  center 
in  the  Thalamus,  114,  150, 
163,  164,  167,  208,  210,  212, 
284,  306 


Body,  geniculate,  medial  (corpus 
gcniculatum  mediale,  internal 
geniculate  body),  an  auditory 
center  in  the  Thalamus,  114, 
118,  121,  154,  157,  163,  164, 
167,  185,  201,  202,  306 

habenular.    See  Habenula. 

of  LuYS,  167,  306 

mammillary  (corpus  mamillarc, 
corpus  candicans),  one  of  a  pair 
of  eminences  at  the  posterior 
end  of  the  Tuber  cinerium  in 
the  Hypothalamus;  an  olfac- 
tory center,  114,  120,  163,  165, 
166,  167,  210,  220,  306 

of  NissL.  See  Substance,  chromo- 
philic. 

pineal  (corpus  pineale,  pineal 
gland,  epiphysis,  conarium),  a 
glandular  outgrowth  from  the 
Epithalamus;  in  some  lower 
vertebrates  it  takes  the  form  of 
a  median  dorsal  eye.  See 
Parietal  eye,  110,  114,  118,  119, 
162,  164,  167,  212 

pituitary.    See  Hypophysis. 

quadrigeminal.  See  Corpora  quad- 
rigemina. 

restiform.  See  Corpus  resti- 
forme. 

striate.     See  Corpus  striatum. 

tigroid.  See  Substance,  chromo- 
phiUc. 

trapezoid  (corpus  trapezoideum), 
transverse  decussating  fibers  in 
the  ventral  part  of  the  medulla 
oblongata  which  connect  the 
auditory  nuclei  of  one  side  with 
the  lateral  Lemniscus  of  the 
other  side,  50,  201 
BoLK,  L.,  193 

Bolton,  J.  S.,  273,  277,  289,  290 
Bonnet,  R.,  81 

Brachium,  of  colliculus  inferior.  See 
Brachium  quadrigeminum  in- 
ferius. 

conjunctivum  (prepcdunclc),  the 
superior  or  anterior  peduncle  of 
the  cerebellum;  rf.  Peduncle, 
cerebellar,  114,  131,  15S,  162, 
165,  176,  187,  188 

pontis  (medipcduncle,  processus 
cerebelli  ad  pontem),  the  middle 
peduncle  of  the  cerebellum;  cf. 


320 


INDEX    AND    GLOSSARY 


Peduncle,    cerebellar,    114,    122, 
158,  162,  187,  188,  192 
Brachium,  quadrigeminum  inferius 
(brachium   of  colliculus  inferior), 
a  ridge  on    the    Corpora   quadri- 
gemina  formed  by  fibers  from  the 
Colliculus  inferior  to  the   medial 
geniculate   Body,    114,    161,    164, 
185 
Brain  (encephalon),  that  portion  of 
the  central  nervous  system  con- 
tained within  the  skull,  106 
development  of.    See  Nervous  sys- 
tem, development  of. 
measurements  of,  123 
new.     See  Neencephalon. 
nomenclature    of.      See    Nervous 

system,  nomenclature  of. 
old.     See  Palseencephalon. 
stem,  all  of  the  brain  except  the 
cerebellum   and  the  cerebral 
cortex,  i.   e.,   the  Segmental 
apparatus,  113,  114,  115,  123, 
164,  181,  185,  186,  192,  266, 
280 
reflexes    of.      See    Reflexes    of 
brain  stem, 
terminology  of.    See  Nervous  sys- 
tem, nomenclature  of. 
weight  of,  123 
Branch.     See  Ramus. 
Branchial    ganglia.      See    Ganglion, 
branchial, 
nerves.     See  Gills,  innervation  of. 
Bridge.     See  Pons. 
Broca,  p.,  292 
Broca's  area.     See  Area  parolfac- 

toria  of  Broca. 
Broca's  convolution,  the  posterior 
part  of  the  gyrus  frontalis  inferior, 
supposed  to  function  as  a  motor 
correlation  center  of  speech,  283, 
292  293 
Brodmann,  K.,  269,  270,  272,  273- 

278,  287,  290 
Bronchial  tubes,  nerves  of,  226,  238 
Brouwer,  B.,  142,  172 
Bruce,  A.,  142 
Bruce,  A.  N.,  130,  142,  193 
Buchanan,  Florence,  98,  105 
Bulb   (bulbus),  any  bulb-like  struc- 
ture; specifically  the  Medulla  ob- 
longata,  as   in   bulbar    paralysis, 
tractus  bulbo-spinalis. 


Bulb,  olfactory,  a  protuberance  from 
the  cerebral  hemisphere  contain- 
ing the  primary  olfactory  center, 
110,  111,  112,  120,  165,  215,  216, 
217,  218,  219,  264 

Bulbar  formation.  See  Formatio 
bulbaris. 

Bundle.     See  Tract  and  Fasciculus. 
basis,    fundamental,    or    ground. 

See  Fasciculus  proprius. 
longitudinal  medial.    See  Fascicu- 
lus longitudinalis  medialis. 
posterior  longitudinal.     See  Fas- 
ciculus longitudinalis  medialis. 
solitary.    See  Fasciculus  solitarius. 

Burdach,  column  of.  See  Fascicu- 
lus cuneatus. 

Burnett,  T.  C.,  279,  299 


Cajal.     See  Ramon  y  Cajal. 
Cajal,  commissural  nucleus  of.    See 

Nucleus,  commissural,  of  Cajal. 
Calcar  avis  (hippocampus  minor),  a 
projection  into  the  posterior  horn 
of  the  lateral  ventricle  formed  by 
the  calcarine  fissure. 
Campbell,  A.  W.,  273,  278 
Canal,  central  (canalis  centralis),  the 
ventricle  of  the  spinal  cord,  126, 
129 
lateral  line.      See  Organs,  lateral 

line, 
neural,  the  lumen  of  the  embry- 
onic Neural  tube ;  also  applied  to 
the  spinal  Canal  of  the  vertebral 
column, 
semicircular     (ductus     semicircu- 
laris).     See  also  Vestibular  ap- 
paratus,   HI,    183,    184,    187, 
195,  196,  201 
spinal,  the  canal  in  the  vertebral 
column   containing    the    Spinal 
cord. 
Cannon,  W.  B.,  240,  241,  248,  255, 

256,  262 
Capps,  J.  A.,  250,  252 
Capsule,  external  (capsula  externa), 
a  thin  band  of  nerve-fibers  form- 
ing   the    outer    border    of    the 
Corpus  striatum,  166,  169,  170 
internal  (capsula  interna),  a  strong 
band     of    nerve-fibers    passing 
through   the   Corpus   striatvun, 


INDEX    AND    GLOSSARY 


321 


144,  165,  166,  1G9,  170,  174,  176, 
210,  253,  2G6,  287 
Capsule,  nasal,  110,  111 
Carbon    dioxid,    production    of,    in 
neurons,  96,  97,  103 
as  respiratory  stimulus,  238,  240 
Carlson,  A.  J.,  240,  241,  247 
Carp,  nervous  system  of,  45,  245, 

302,  303 
Carpiodes   tumidus,   brain   of,   302, 

303 
Cat,  nervous  system  of,  90,  251 
Catfish,  nerves  of,  245,  246 
Cauda  equina,  a  bundle  of  elongated 
spinal  nerve  roots  arising  from  the 
lumbar  and  sacral  segments  of  the 
spinal  cord. 
Caudal,   pertaining   to   the   tail,    or 
directed  toward  the  tail  end  of  the 
body,'  as  opposed  to  cephalic,  116 
Cavum    septi    pellucidi    (fifth    ven- 
tricle, pseudocoele),  the  space  en- 
closed between  the  Septum  pellu- 
cidum  of  the  two  cerebral  hemi- 
spheres; not  a  true  ventricle,  162 
Cell  (or  cells),  auditory  (hair  cells  of 
organ  of  Corti),  197,  198,  199 
basket,  of  cerebellum,  52,  190, 191, 

192 
of  Betz  (giant  pyramidal  cells  of 
motor  center  of  cerebral  cortex), 
274,  283,  284,  285 
body,  the  nucleus  and  perykaryon 

of  a  neuron,  39 
of  Claudius,  197 
of    Corti    (hair  cells),    197,   198, 

199 
of  Deiters  of  organ  of  Corti,  197 
ependyma.     See  Ependjrma. 
granule,  of  cerebellar  cortex,  190, 
191,  192 
of  cerebral  cortex,  274,  290 
of  olfactory  bulb,  217,  218 
of  retina,  206,  207 
of  Hensen,  197 
mitral,  an  olfactory  neurone  of  the 

second  order,  217,  218 
nerve.     See  Neuron, 
neuroglia.     See  Neuroglia, 
of    PuRKiNJE.       See    Purkinje, 
cells  of. 
Cellulifugal,  conducting  away  from 
the  Cell  body,  applied  to  the  proc- 
esses of  a  neuron. 

21 


Cellulipetal,  conducting  toward  the 
Cell  body,  applied  to  the  yjrocesses 
of  a  neuron- 
Center    (centrum),    a    collection    of 
nerve    cells    concerned    with    a 
particular  function,  25,  106,  108, 
109,  181,  302 
association.     See  also  Center,  cor- 
tical,  association,   64,   65,    103, 
104,  181,  258,  294,  302,  304 
auditory.       See    Area,     acoustic, 
Auditory  apparatus,  and  Center, 
cortical,  auditory, 
correlation,    108,    109,    113,    120, 

133,  158,  181,  186,  304 
cortical,    a   part   of    the   cerebral 
cortex  which  can  be  differen- 
tiated   functionally  f-i-om    its 
neighbors;  cf.  Area,  cortical. 
These  centers  are  sometimes 
called  areas,  fields,  spheres,  or 
zones,  273,  282,  283 
association,  104,  181,  273,  284, 
285,  287,  288,  289,  290,  292, 
306,  311,  312 
auditorv,  166,  202,  273,  283 
gustatory,  246,  288 
motor,  140,  141,  181,  187,  273, 
281,  282,  283,  284,  285,  292, 
306 
olfactory.    See  Archipalliiun. 
optic.       See    Center,     cortical, 

visual, 
projection.    See  Projection  cen- 
ter, 
of  reading.    See  Speech,  appara- 
tus of. 
somesthetic,  141,  166,  177,  253, 

273,  282,  283,  284,  285,  288 
of  speech.    See  Speech,  appara- 
tus of. 
tactile.      See    Center,    cortical, 

somesthetic. 
of    temperature.      See    Center, 

cortical,  somesthetic. 
visual,  166,  210,  267,  268,  273, 

283,  284,  288 
of  writing.    See  Speech,  appara- 
tus of. 
motor.    See  Motor  apparatus  and 

Center,  cortical,  motor, 
optic.     Sec  Visual  apparatus  and 

Center,  cortical,  visual, 
oval.    See  Center,  semioval. 


322 


INDEX    AND    GLOSSARY 


Center  for  pain.  See  Thalamus, 
pain  center  in. 

primary,  109,  143,  151 

projection,  See  Projection  cen- 
ters. 

reflex.      See    also   Reflex   circuit, 

109,  113,  129,  156 
respiratory,  237,  238,  239,  240 
semioval  (centrum  semiovale,  cen- 
trum ovale),  the  great  mass  of 
white  matter  in  the  center  of 
each  cerebral  hemisphere. 

sensory,  117,  120 
tactile.       See     Area,     cutaneous. 
Touch,  apparatus  of,  and  Cen- 
ter, cortical,  somesthetic. 
trophic,     a     nerve-center     which 
regulates  the  nutrition  of    an- 
other part,  109 
of  trunk  and  limb  reflexes,  129 
vasomotor.      See   Vasomotor   ap- 
paratus. 
visceral.     See  Area,  visceral, 
visual.    See  Visual  apparatus  and 
Center,  cortical,  visual. 
Central-  nervous  system.     See  Ner- 
vous system,  central, 
pause,  98 
Centrifugal.     See  Efferent. 
Centripetal.     See  Afferent. 
Centrum.     See  Center. 
Cephalic,  pertaining  to  the  head,  or 
directed  toward  the  head  end  of 
the  body,  as  opposed  to  caudal, 
116 
Cerebellum,  the  massive  coordina- 
tion center  dorsally  of  the  upper 
end  of  the  Medulla  oblongata, 

110,  111,  112,  115,  117-120, 
120-122,  143,  152,  158,  186-194, 
264 

cortex  of.  See  Cortex,  cerebellar, 
development  of,  117,  118,  119,  187 
fiber  tracts  of,  130,  137,  158,  176, 

187   188 
functions  of,  186, 189, 192,  289,  305 
lesions  of,  189 

Cerebration,  unconscious,  297,  309, 
311 

Cerebrum,  that  portion  of  the  brain 
lying  above  the  Isthmus ;  also  used 
as  synonymous  with  Prosen- 
cephalon and  Cerebral  hemi- 
spheres, 121,  122,  143,  160 


Chain,  sympathetic.  See  Trunk, 
sympathetic. 

Chemical  processes    in    nerve-cells, 
96,  97,  99 
sensibility,  72,  85 

Chiasma,  optic  (chiasma  opticimi), 
the  partial  decussation  of  the 
optic  Tracts  on  the  ventral  surface 
of  the  brain,  118,  119,  120,  208, 
209,  210 

Child,  C.  M.,  31,  36,  97,  105 

Chimpanzee,  cerebral  cortex  of,  282 

Chorda  tympani,  146,  245 

Chorioid  plexus  (choroid  jjlexus) .  See 
Plexus,  chorioid. 

Chrionomus  plumosos,  nervous  sys- 
tem of,  30 

Chromatin,  a  nucleo-protein  sub- 
stance found  in  the  cell  nucleus,  99 

Chromatolysis,  the  solution  and  dis- 
appearance of  the  chromophilic 
Substance  from  a  neuron,  48,  49, 
136,  284 

Chromophilic  bodies,  granules,  or 
substance.  See  Substance,  chro- 
mophilic. 

Ciliary  process.    See  Process,  ciliary. 

Cingulum,  an  association  tract  of  the 
cerebral  hemisphere  lying  under 
the  Gyrus  cinguli,  267 

Circle  of  Willis,  a  polygonal  circuit 
of  anastomosing  arteries  on  the 
ventral  surface  of  the  brain,  from 
which  some  of  the  arteries  of  the 
brain  arise. 

Circuit,  organic.    See  Reflex  circuit. 

Circulation  of  the  blood,  apparatus 
of.  See  also  Vasomotor  apparatus, 
89,  147,  234,  235. 

Clarke,  column  of,  or  dorsal  nucleus 
of.  See  Nucleus,  dorsal,  of  Clarke. 

Claudius,  cells  of,  197 

Claustrum,  a  thin  band  of  gray  mat- 
ter between  the  external  Capsule 
and  the  cortex  of  the  island  of 
Reil,  or  Insula. 

Clava,  an  eminence  on  the  dorsal 
surface  of  the  lower  end  of  the 
medulla  oblongata  produced  by 
the  nucleus  of  the  Fasciculus 
graciUs,  130,  164,  176,  177,  188 

Cochlea,  the  bony  spirally  wound 
canal  containing  the  auditory  re- 
ceptor, 85,  183,  196,  199,  201,"  202 


INDEX    AND    GLOSSARY 


323 


Co-consciousness,  297 
Ca'lenteratcs,  nervous  system  of,  27, 

227 
CoGHiLL,  G.  E.,  6G,  67,  85,  94,  135, 

142,  182 
Cold,  sensations  of.     See  Tempera- 
ture, apparatus  of. 
Cole,  L.  J.,  213 
Colic,  250 
Collateral,  a  small  side  branch  of  an 

Axon,  40,  44 
CoUiculus  facialis  (eminentia  facialis, 
eminentia  abducentis,  eminentia 
teres,  Eminentia  mediaUs),  an 
eminence   in   the   floor    of    the 
fourth    ventricle    produced    by 
the  VII  nucleus  and  the  Genu 
of  the  facial  nerve,  154 
inferior,  one  of  the  lower  pair  of 
Corpora  quadrigemina,  contain- 
ing chiefly  reflex  auditory  cen- 
ters,   114,    154,   157,    160,    164, 
174,  176,  185,  201,  202 
superior  (optic  lobe,  optic  tectum, 
nates),  one  of  the  upper  pair  of 
Corpora  quadrigemina,  contain- 
ing chiefly  reflex  optic  centers, 
62,  63,  lil,  112,  114,  150,  154, 
160,  161,  164,  185,  208,  209,  210, 
211,  264 
Collins,  J.,  233 
Colon,  242 

Column,    anterior.      See    Funiculus 
ventralis. 
of     BuRDACH.       See     Fasciculus 

cuneatus. 
of  Clarke.     See  Nucleus,  dorsal, 

of  Clarke. 
dorsal    (coliunna    dorsalis    grisea. 
See  Column,  gray.     This  name 
is   also    applied  to    the   dorsal 
Funiculus),   126,   127,   128-130, 
133,  150,  151,  178,  251 
of  Fornix.     See  Fornix  column, 
fundamental.    See  Fasciculus  pro- 

prius. 
of  GoLL.  See  Fasciculus  gracilis, 
gray  (columna  grisea),  one  of  the 
longitudinal  columns  of  neurones 
which  make  up  the  gray  matter 
of  the  spinal  cord.  There  are 
three  columns:  (1)  dorsal  (pos- 
terior), (2)  ventral  (anterior), 
and  (3)  lateral  (middle  or  inter- 


mediate).     These    columns    were 

formerly   called   horns     (cornua); 

cf.  also  Funiculus,  126,  127,  128, 

130,  150,  151j 
Column,  intcrmcdio-lateral,  of  spinal 
cord,  229 

lateral  (columna  lateralis  grisea; 
see  Coltmm,  gray),  126,  128, 
150,  151,  229 

of  medulla  oblongata,  151-156 

posterior.     See  Funiculus,  dorsal. 

somatic  motor,  150-156 
sensory,  150-156 

of  TtJRCK,  the  ventral  cortico- 
spinal Tract. 

ventral  (columna  ventralis  grisea; 
see  Column,  gray.  This  term 
is  also  applied  to  the  ventral 
Funiculus),  126,  127,  128,  129, 
130,  133,  150,  151 

vesicular.  See  Nucleus,  dorsal,  of 
Clarke. 

visceral  motor,  150-156 
sensory,  150-156 
Columna.     See  Column. 
Coma,  297 
Comma    tract    of    Schultze.      See 

Fasciculus  interfascicularis. 
Commissure  (conmaissura) ,  a  band 
of  fibers  connecting  correspond- 
ing parts  of  the  central  nervous 
system  across  the  median  plane ; 
many  decussations  are  also 
called  commissures,  265 

anterior  (commissura  anterior), 
fibers  passing  transversely 
through  the  Lamina  terminalis 
and  connecting  the  basal  por- 
tions of  the  two  cerebral  hemi- 
spheres, 114,  162,  165,  222,  265 

dorsal,  fibers  which  cross  the  mid- 
plane  of  the  spinal  cord  dorsally 
of  the  ventricle,  127 

of  fornix.  See  Commissure  of  hip- 
pocampus. 

of  Gttdden.  See  Commissiu'e, 
postoptic. 

habenular  (superior  commissure), 
a  band  of  fibers  connecting  the 
two  Habenulae  immediately  in 
front  of  the  pineal  Body,  265 

of  hippocampus  (conunissura  hip- 
pocampi, commissura  fornicis), 
fibers    connecting    the    Hippo- 


324 


INDEX    AND    GLOSSARY 


campi  of  the  two   sides  through 
the  Fornix  body,   170,  220,   265, 
266 
Commissure,   inferior.      See    Com- 
missure, postoptic. 
of  Meynert.     See  Commissure, 

postoptic. 
middle.    See  Massa  intermedia. 
mollis.    See  Massa  intermedia, 
posterior   (commissura  posterior), 
fibers       passing       transversely 
through  the  anterior  end  of  the 
roof  of  the  midbrain,  162,  220 
postoptic     (inferior    commissure), 
fibers  passing  transversely  across 
the  floor  of  the  hypothalamus 
associated  with  the  optic  chias- 
ma ;  contains  the  commissures  of 
GuDDEN,  Meynert,  and  other 
fibers,  265 
soft.     See  Massa  intermedia, 
superior.    See  Commissure,  habe- 

nular. 
of     tectum     (commissura     tecti), 
fibers  passing  transversely  across 
the  roof  of  the  midbrain,  con- 
tinuing   backward    the    Com- 
missura posterior,  161 
ventral,    fibers    which    cross    the 
midplane  of  the  nervous  system 
ventrally  of  the  ventricle,  127, 
129,  131,  133,  265 
Compensation  of  function  in  cortex, 

294 
Components  of  nerves.    See  System, 

functional. 
Conarium.     See  Body,  pineal. 
Conduct,  neurological  basis  of,  262, 

312-316 
Conduction,  avalanche,  the  summa- 
tion of  nervous  impulses  in  a 
center    so    as    to    increase    the 
intensity     of     discharge,     101, 
192 
nervous,  38,  54,  96,  97,  98,  101 
Cones  of  retina,  205,  206,  207,  208, 

211 
Conflict  in  evolution,  314 
Conjunctiva,  84,  85,  250 
Consciousness,  dissociation  of,  297 
evolution  of.    See  Psychogenesis. 
of  lower  animals;  cf.  Psychogene- 
sis, 32,  257,  305 
multiple,  297 


Consciousness,  neurological  mechan- 
ism of,  104,  166,  224,  242,  249, 
258,    259,    260,    261,   280,   281, 
286,  287,  290-297,  305-316 
seat  of,  291 
of  self,  314 
Continuity  of  consciousness,  297 
Convolution.     See  Gyrus. 

of  Broca.     See  Broca's  convolu- 
tion. 
Coordination,    the    combination    of 
nervous   impulses   in  motor   cen- 
ters to  ensure  the  cooperation  of 
the  appropriate  muscles  in  a  re- 
action, 35,  130,  132,  133,  181 
Cornea,  84,  85,  249 
Cornu.     See  Horn. 
Corona  radiata,  the  Projection  fibers 
which  radiate  from  the  internal 
Capsule   into  the  cerebral  hemi- 
sphere, 164, 166,  169,  170,  266,  287 
Corpora    quadrigemina,    the    dorsal 
part  of  the  Mesencephalon,  con- 
taining the  superior  and  inferior 
CollicuU,  118,  119,  121,    160,  162, 
201,  210 
Corpus   callosum,   a  large  band  of 
commissural    fibers    connecting 
the  Neopallium  of  the  two  cere- 
bral hemispheres,  119,  162,  165, 
166,  170,  220,  265,  266,  267 
candicans.     See    Body,    mammil- 

lary. 
dentatum.     See  Nucleus,  dentate, 
fornicis.     See  Fornix  body. 
geniculatum.     See  Body,  genicu- 
late, 
mamillare.      See  Body,   mammil- 

lary. 
pineale.     See  Body,  pineal. 
ponto-bulbare,  114 
quadrigeminum.       See      Corpora 

quadrigemina. 
restiforme  (restiform  body),  the 
inferior  peduncle  of  the  cerebel- 
lum; cf.  Peduncle,  cerebellar, 
130,  155, 156,  158,  176,  187,  188, 
192,  201 
striatum  (striate  body),  a  subcor- 
tical or  basal  mass  of  gray  and 
white  matter  in  each  cerebral 
hemisphere,  116,  117,  118,  123, 
162,  165,  166,  167,  168,  169, 
170,  174,  176,  215,  264,  287 


INDEX    AND    GLOSSARY 


325 


Corpus    trapczoideum.      See  Body, 

trapezoid. 
Correlation,  the  combination  of  ner- 
vous impulses  in  sensory  centers 
resulting  in  adaptive  reactions,  35, 
38,  43,  106,  133,  181 
Correlation  neurone,  62,  133,  134 
Cortex,    cerebellar,    the    superficial 
gray  matter  of  the  cerebellum, 
51,  52,  189-192 
compared  with  cerebral  cortex, 

186,  189,  192,  289,  305,  308 
localization  of  function  in,  189, 

281,  305 
neurones  of,  51,  52,  190 
cerebral   (pallium,  mantle),  asso- 
ciation   tissue    forming    the 
superficial  gray  matter  of  the 
cerebral  hemisphere,   26,   65, 
74,    109,    116-119,    123,    141, 
166,  266-316 
areas  of.    See  Area,  cortical, 
centers  of.    See  Center,  cortical, 
dependencies  of,  114,  115 
development  of,   116-119,  286, 

287,  288,  289,  290 
electric  excitability  of,  281 
evolution  of.     See  also  Hemi- 
spheres, cerebral,  comparative 
anatomy    and    evolution    of, 
115,  129,  263,  280,  301 
functions  of,  104,  115,  122,  186, 

189,  192,  254,  279-316,  311 
layers  of.    See  Layers  of  cerebral 

cortex, 
lesions  of,  254,  275,  279,  280, 

283,  284,  286,  290-294 
localization  of  function  in.    See 
Localization    of    function    in 
cerebral  cortex,  and  Center, 
cortical, 
motor  centers  of.     See  Center, 

cortical,  motor, 
neurones   of,   42,   44,   268-274, 

290 
number  of  neurons  in,  26 
phylogeny  of.    See  Cortex,  cere- 
bral, evolution  of. 
structure  of,  263-277 
somatic.    See  Neopallium. 
CoRTi,  cells  of  (hair  cells),  197,  198, 
199 
ganglion  of.    See  Ganglion,  spiral, 
organ  of.    See  Organ,  spiral. 


CoRTi,  rod  of,  197,  198 

tunnel  of,  197 
Cough,  mechanism  of,  238,  239 
Crista  ampullaris,  196,  198 

basilaris  of  cochlea,  197 
Cms,  a  stalk  or  peduncle,  applied  to 
compact  masses  of  fibers  which 
connect   different   parts   of   the 
brain;  cf.  Peduncle. 

commune,  of  internal  ear,  196 

flocculi,  114 

fornicis.    See  Fornix,  crus  of. 

olfactoria,  the  stalk  or  peduncle  of 
the  Olfactory  bulb. 
Crusta.     See  Basis  peduncuU. 
Crustaceans,  nervous  system  of,  29 
Cuneus,  a  wedge-shaped  gyi'us  on  the 

medial  face  of  the  posterior  pole 

of  the  cerebral  hemisphere  receiv- 
ing visual  projection  fibers,   119, 

17b,  210 
Cup,  optic.    See  also  Vesicle,  optic, 

204 
Cui-iosity,  314 

CusHiNG,  H.,  243,  245,  248,  286,  299 
Cyon,  nerve  of,  235 
Cytoplasm,  all  protoplasm  of  a  cell 

exclusive  of  that  in  the  nucleus, 

39,  96,  99,  102 


Davies,  H.  M.,  79,  84,  95,  172 
Dearborn,  G.  V.  N.,  310 
Decussation  (decussatio),  a  band  of 
fibers  crossing  the  median  plane 
of  the  central  nervous  system 
and  connecting  unlike  centers  of 
the  two  sides;  many  decussations 
are  called  commissures, 
of  FoREL.     See  Decussation,  teg- 
mental, ventral, 
fountain.     See  Decussation,   teg- 
mental, dorsal, 
of   Meynert.      See   Decussation, 

tegmental,  dorsal, 
optic.     See  Chiasma,  optic. 
of  pyramids,  131 

tegmental,     dorsal     (Meynert's 
decussation,    fountain   decus- 
sation), 161 
ventral    (Forel's   decussation), 
161 
Degeneration  of  nervous  tissues,  46, 
48,  55,  135,  136,  283,  290 


326 


INDEX    AND    GLOSSARY 


Degeneration,  sclerotic,  of  cortex, 
284 

Deiters,  cells  of,  in  spiral  Organ,  197 
vestibular  nucleus  of,  184,  185 

Dejbrine,  J.  J.,  287 

Dementia,  290 

Dendrite,  a  process  of  a  Neuron  which 
conducts  toward  the  cell  body,  39, 
40,  41,  44,  45,  47,  96,  103,  104 

Dependency,  cortical,  a  part  of  the 
brain  stem  developed  as  a  sub- 
sidiary of  the  cerebral  cortex,  212, 
263,  305 

Depression,  101,  102,  103 

Development  of  the  nervous  system. 
See  Nervous  system,  development 
of. 

Dewey,  J.,  20,  61,  67,  308,  309,  311 

DeWitt,  Ltdia  M.  a.,  87,  90,  95 

Diaphragm,  innervation  of,  236, 
237-240 

Diaschisis,  a  transitory  defect  of 
function  due  to  disturbance  of 
cortical  equilibrium,  292,  293,  294 

Diencephalon  (betweenbrain,  thala- 
mencephalon),  the  brain  region 
lying  between  Mesencephalon 
and  Telencephalon;  sometimes 
called  Thalamus  or  Optic  thala- 
mus, but  properly  divided  into 
Thalamus,  Epithalamus,  and 
Hypothalamus,  116-119,  121, 
122,  160-167 
development  of,  116-119 

Diffusion  of  nerve  impulses,  104,  192 

Digestion,  apparatus  of,  78, 224, 232, 
240-243,  255,  256 

Dilemma,  58,  307 

Dioptric  apparatus  of  eyeball,  205 

Disagreeable  and  agreeable.  See 
Affection. 

Discrimination.  See  Reaction,  dis- 
criminative. 

Dissociation  of  consciousness,  297 

Distention,  sensations  of,  89 

Dog,  functions  of  cortex  of,  279,  281, 
286 
scratch  reflex  of,  134 

Dogfish,  nervous  system  of.  See 
Fishes,  nervous  system  of. 

Dogiel,  a.  S.,  83,  84,  85,  228,  233 

DoLLEY,  D.  H.,  101,  102,  103,  105 

Dolphin,  absence  of  olfactory  organs 
of,  216 


Donaldson,  H.  H.,  105,  123,  124 
Dorsal,  on  the  back  side  of  the  body, 

termed  posterior  in  the  B.  N.  A. 

lists,  116 
Ductus  cochlearis,  195,  196,  197,  198 

endolymphaticus,  195,  196 

reuniens,  196 

semicircularis.  See  Canal,  semi- 
circular, and  Vestibular  appara- 
tus. 

utriculo-saccularis,  196 
Dura  mater,  the  outer  brain  mem- 
brane, 38 
DuRUPT,  A.,  193 
Dynamic    theory    of    consciousness, 

293,  296 

Ear.      See  Auditory  apparatus  and 
Vestibular  apparatus, 
brain,  112,  123 
evolution  of,  199,  201 
Earthworm,  nervous  system  of,  28 
Ectoderm  (epiblast),  the  outer  germ 
layer  of  the  embryo,  from  which 
the  epidermis  and  the  Neural  tube 
develop,  204 
Edgeworth,  F.  H.,  180 
Edinger,  L.,  36,  115.  124,  159,  219, 

223,  280,  299,  306 
Edinger-Westphal,  nucleus  of  (the 
visceral  efferent  nucleus  of  the  III 
nerve;  cf.  Nucleus  of  oculomotor 
nerve). 
Education,  32,  312-316 
Effector,  an  organ  of  response,  26,  92 
Efferent,   conducting   away  from  a 
center,  25,  42,  108,  126,  137,  145- 
150 
Electric  excitability  of  nervous  tis- 
sues, 281,  283,  286 
phenomena     in     nervous     tissue, 
96 
Embryology  of  nervous  system,    See 

Nervous  system,  embryology  of. 
Eminentia    abducentis.      See    Col- 
Uculus  facialis. 
facialis.    See  CoUiculus  facialis. 
hypoglossi.     See  Trigonum  hypo- 

glossi. 
medialis  (eminentia  teres),  a 
medial  longitudinal  ridge  in  the 
floor  of  the  fourth  ventricle;  an 
enlarged  portion  is  the  CoUicu- 
lus facialis. 


INDEX    AND    GLOSSARY 


327 


Eminentia    teres.       See    Eminentia 
medialis. 
vagi.     See  Ala  cinerea. 

Emotion.     See  Ali'ection. 

Empis  stercorea,  nervous  system  of, 
30 

Encephalon,  the  brain,  120 

Enclolymph,.196,  19S 

End-organ,  the  peripheral  apparatus 
related  to  a  nerve;  a  Receptor  or 
Effector,  25,  40,  70,  79,  98 

End-plate,  motor,  the  terminal  ar- 
borization of  a  motor  axon  upon  a 
muscle-fiber,  40,  92,  101 

Endyma.     See  Ependjona. 

Engram,  295 

Environment,  17,  IS,  69,  312 

Epencephalon,  the  cerebellum. 

Ependyma  (endj-ma),  the  Uning 
membrane  of  the  ventricles  of  the 
brain,  derived  from  the  original 
epithelium  of  the  Neural  tube,  38 

Epiblast.     See  Ectoderm. 

Epicritic  sensibility,  a  highly  refined 
type  of  cutaneous  sensibiUty,  espe- 
cially on  hairless  parts,  84,  85,  132 

Epiglottis,  organs  of  taste  upon,  147, 
243 

E]iinephrin.     See  Adrenalin. 

Epiphysis.     See  Body,  pineal. 

Epithalamus,  the  dorsal  subdivision 
of  the  Diencephalon,  containing 
the  pineal  Body  and  the  Haben- 
ula,  an  important  olfactory  correla- 
tion center,  111,  112,  il8,  119, 
121,  122,  162,  165,  167,  220,  221, 
222 

Epithelium,  a  thin  sheet  of  cells,  24 
nerve  endings  in,  90 
olfactory       (Schneiderian     mem- 
brane), 217 

Equihbrium,  apparatus  of.    See  also 
Vestibular    apparatus,    77,    88, 
89,  147,  183,  186,  199,  200 
nervous,  66,  293,  296 
theorv  of  consciousness,  296 

E.sophagus,  78,  90,  144,  147,  234,  242 

Esthetic  experience.     See  Affection. 

Ethics.     See  Morals. 

Eugenics,  312 

Eustachean  tube  (auditory  tube), 
195 

Evolution  of  mind.  See  Psycho- 
genesis. 


Evolution  of  Nervous  system.    See 

Nervous  system',  evolution  of. 
EwALD,  J.  R.,  184,  203 
Excitability,   electric.     See  Electric 

excitability  of  nervous  tissues. 
Excitation,  fatigue  of,  101,  102,  103 
Experience,  learning  by,  34,  294,  307, 

308,  312,  315 
Exteroceptor,  a  sense  organ  excited 

by  stimuli  arising  outside  the  body, 

74,  77,  79 
Exteroceptors,    apparatus    of,    132, 

137,  138,  139,  141,  145,  163-167, 

172-174,  250 
Extii-pation  of  cortical  centers,  286 
Eye.     See  Visual  apparatus. 

accommodation  of.     See  Accom- 
modation of  vision. 

brain  (ophthaLmencephalon),  112, 
123 

conjugate  movements  of,  186,  211, 
283 

development  of,  116,  117,  204 

evolution  of,  212 

muscles  of,  92,  110,  143,  146,  148, 
ISO,  232,  247 

parietal.     See  Parietal  eye. 

pineal.     See  Parietal  eye. 


Face  brain,  123 

Faculties,  mental,  280,  285,  290,  291 
Falx  cerebri,  a  longitudinal  fold  of 
Dura    mater    which    extends    be- 
tween the  cerebral  hemispheres  in 
the  longitudinal  fissure. 
Fascia  dentata.     See  Gyrus  denta- 

tus. 
Fasciculus,  a  bundle  of  nerve-fibers 
not  necessarity  of  similar  func- 
tional  connections.     The   term 
is    often    used,    however,   as    a 
synonjTU  for  Tract,  128. 
antero-laterahs     superficialis     (of 
'  GowERs).     See  Fasciculus  ven- 

tro-lateralis  superficiaUs. 
ccrebello-spinalis.        See      Tract, 

spino-ccrebollar. 
cerebro-spinalis.         See       Tract, 

cortico-spinal. 
circumolivaris  p^Tamidis,  114 
communis,   a  name  formerly  ap- 
plied to  the  Fasciculus  solita- 
rius  in  lower  vertebrate  brains. 


328 


INDEX    AND    GLOSSARY 


Fasciculus  cuneatus  (column  of  Bur- 
dach),  the  lateral  portion  of 
the  dorsal  funiculus  of  the 
spmal  cord,  128, 130, 139, 176, 
177 
nucleus  of.  See  Tuberculum 
cuneatum. 

dorso-lateralis  (Lissauer's  zone, 
Lissauer's  tract),  130 

of  GowERS.  See  Fasciculus 
ventro-lateralis  superficialis. 

gracilis    (column    of    Goll),    the 
medial  portion  of  the  dorsal 
Funiculus  of  the  spinal  cord, 
128,  130,  139,  176,  177 
nucleus  of.     See  Clava. 

inner  spiral,  of  Spiral  organ,  197 

interfascicularis  (comma  tract, 
tract  of  Schultze),  130,  131 

longitudinahs  inferior  of  cerebral 
hemisphere,  222,  267 

longitudinalis  medialis  (medial 
longitudinal  bundle,  posterior 
longitudinal  bundle,  fasciculus 
longitudinalis  posterior  or  dorsa- 
lis),  a  bundle  of  motor  coordina- 
tion fibers  running  through  the 
brain  stem,  131,  152,  155,  156, 
161,  176,  181,  185,  201,  211 

longitudinalis  superior  of  cerebral 
hemisphere,  267 

marginalis  ven trails,  131 

of  Meynert.  See  Tract,  haben- 
ulo-peduncular. 

occipito-frontalis  inferior  of  cere- 
bral hemisphere,  267 

proprius  of  cerebral  hemisphere. 
See  Fibers,  arcuate  (1). 

proprius  of  spinal  cord  (funda- 
mental columns,  basis  bundles, 
ground  bundles) ,  that  portion  of 
the  white  matter  of  the  spinal 
cord  which  borders  the  gray 
matter  and  contains  correla- 
tion fibers;  arranged  in  dorsal, 
lateral,  and  ventral  subdivi- 
sions, 127,  130,  131,  133,  179, 
182,  251,  252,  253,  258 

retrofiexus  of  Meynert.  See 
Tract,  habenulo-peduncular. 

solitarius  (tractus  solitarius,  soli- 
tary bundle,  in  lower  verte- 
brates often  called  fasciculus 
communis),       a       longitudinal 


bundle  of  fibers  in  the  medulla 
oblongata  containing  the  central 
courses  of  the  visceral  sensory 
root-fibers  of  the  cranial  nerves, 
149,  150,  155,  156,  164,  234, 
237,  239,  240,  241,  244,  247 
Fasciculus  sulco-marginalis,  130, 
131 
thalamo-mamillaris.       See  Tract, 

mamillo-thalamic . 
transversus  occipitalis  of  cerebral 

hemisphere,  267 
uncinatus  of  cerebral  hemisphere, 

267 

ventro-lateralis    superficialis    (an- 

tero-lateral  fasciculus,  Gowers' 

tract),  128,  130 

Fatigue,  101-103,  255,  256,  258,  304 

Fear.     See  also  Affection,  89,  255, 

256. 
Feeble-mindedness.     See  Idiocy. 
Feeding,  reflexes  of.    See  Reflexes  of 

feeding. 
Feeling  (affective).    See  Affection. 
Feeling  tone.    See  also  Affection,  249, 

254,  258-262 
Ferrier,  D.,  194 

Fiber,  or  fibers,  fibr£e.     See  Nerve- 
fiber, 
arcuate,    of    the    cerebral    hemi- 
sphere,      short      association 
fibers  connecting  neighboring 
gyri;  also  called  fibra?  propria^ 
and  fascicuU  proprii,  267,  285 
of  the  meduUa  oblongata,  decus- 
sating fibers  lying  in  a  super- 
ficial series  (external  arcuate 
fibers)  and  a  deep  series  (in- 
ternal arcuate  fibers),  155 
association;  cf.  Tract,  association, 
266,  267,  269,  285,  287,  291-293 
of  MtJLLER,  205,  206 
postganglionic.    See  Neuron,  post- 
ganglionic. 
preganglionic.     See  Neuron,  pre- 
ganglionic. 
projection.    See  Projection  fibers, 
propriae    (arcuate    fibers    of    the 
cerebral  hemisphere),  267,  285 
Field,  auditory  psychic,  285 

cortical,  a  term  sometimes  used  as 
a  synonym  of  Center,  cortical,  or 
of  Area,  cortical. 
visual  psychic,  285 


INDEX    AND    GLOSSARY 


329 


Fila     olfactoria,     the;     iilaincnts    of 

which  the  olfactory  nerve  is  com- 
posed, 146,  217 
Fillet.     See  Lemniscus. 
Filum  terminale  (terminal  filament), 

the  slender  caudal  termination  of 

the  spinal  cord,  107 
Fimbria,    a    band    of    fibers    which 

borders     the     Hippocampus     and 

joins   the  Fornix,    165,   220,   221, 

222,  2G5 
Final  common  path,  58,  59,  62,  101, 

258 
Fischer,  B.,  280,  299 
Fishes,  nervous  system  of,  109,  110, 

111,  112,  122,  123,  148-153,  166, 

179-181,  187,  199,  200,  201,  212, 

215,  237,  240,  245,  246,  279,  302, 

303 
Fissure  (fissura),  in  the  cerebral  cor- 
tex a  deep  fold  which  involves 
the  entire  thickness  of  the  brain 
wall;  cf.  Sulcus.  This  is  the 
usage  of  the  B.  N.  A.,  but  fissure 
and  sulcus  are  often  used  as 
synonyms  and  the  B.  N.  A.  is 
not  consistent  in  this  matter. 

calcarine,  119,  268 

chorioid,  the  fold  in  the  postero- 
medial wall  of  the  cerebral 
hemisphere  through  which  the 
lateral  chorioid  Plexus  is  in- 
vaginated. 

dorsal,  of  spinal  cord  (dorsal 
median  septum),  128 

ectorhinal.    See  Fovea  limbica. 

hippocampal,  221,  222 

lateral  (fissura  lateralis  Sylvii, 
fissure  of  Sylvius),  a  deep  fis- 
sure on  the  lateral  surface  of  the 
cerebral  hemisphere  which  sepa- 
rates the  temporal  from  the 
frontal  and  parietal  lobes,  121, 
166,  266 

longitudinal,  the  great  fissure  be- 
tween the  two  cerebral  hemi- 
spheres, 120,  265 

parieto-occipital,  119,  121,  170 

rhinal.     See  Fovea  limbica. 

of  Rolando.  See  Sulcus  cen- 
tralis. 

ventral,  of  spinal  cord,   127,   128, 
129 
Fistula,  gastric,  241 


Fleciisio,  p.,  286,  287,  288,  299 
tract  of.     See  Tract,   spino-cere- 
bellar,  dorsal. 
Flexure,  a  bending  or  crumpling  of 
the  develojjing  Neural  tube  caused 
by  unequid  growth  of  its  parts,  as 
cervical,    pontile,    mesencephalic, 
diencephalic,     and     telencephalic 
flexures,  116-119 
Flies,  nervous  system  of,  30 
Flocculus,  the  most  lateral  lobe  of 

the  cerebellum. 
Flourens,  J.  p.  M.,  240 
Fluid,  cerebro-spinal,  a  clear  liquid 
resembling  lymph  filling  the  ven- 
tricles   of    the    brain    and    spinal 
cord. 
Folium,  one  of  the  leaf-like  subdivi- 
sions   of    the    cerebellar    cortex; 
these  are  termed  Gyri  in  the  B.  N. 
A.,  189 
Foramen  interventriculare  (foramen 
of  Monro,  porta),  the  commu- 
nication   between     the    lateral 
and  the   third   ventricles,    162, 
264 
of  Magendie,  an  aperature  in  the 
membranous  roof  of  the  fourth 
Ventricle, 
of  Monro.     See  Foramen  inter- 
ventriculare. 
Forebrain.     See  Prosencephalon. 
FoREL,  decussation  of.     See  Decus- 
sation, tegmental,  ventral, 
field  of,  167 
Formatio    bulbaris     (bulbar   forma- 
tion), the  tissue  comprising  the 
primary  olfactory  center  in  the 
olfactory  bulb,  i.  e.,  the  Glome- 
ruli, mitral   Cells,  and  granule 
Cells,  220 
reticularis     (reticular     formation, 
processus   reticularis    in    spinal 
cord),  a  mixture  of  nerve-fibers 
and    cell   bodies   providing   for 
local  reflexes,  65,  127,  129,  153, 
156,  157,  158,  174,  176, 181, 184, 
240,  247,  304,  310 
Fornix,  a  complex  fiber  system  con- 
necting the  Hippocampus  with 
other  parts  of   the  brain,    162, 
164,  165,  166,  222 
body  (corinis  fornicis),  the  middle 
part  of  the  Fornix. 


330 


INDEX    AND    GLOSSARY 


Fornix  columns  (columnse  fornicis, 
anterior  pillars  of  fornix),  two 
columnar  masses  of  fibers  diverg- 
ing from  the  anterior  end  of  the 
Fornix  body  to  descend  into  the 
diencephalon,  165,  170,  220,  221 
commissure.     See  Commissure  of 

hippocampus, 
crus    of    (crus   fornicis,    posterior 
pillar  of  fornix),  a  band  of  fibers 
on  each  side  of  the  brain  con- 
necting the  posterior  part  of  the 
Fornix  body  with  the  Fimbria, 
longus  of  FoREL,  fibers  which  per- 
forate the  Corpus  callosum  and 
pass  through  the  Septum  pelluci- 
dtun. 
Fossa  fiocculi,  141 
lateralis    (fossa    of    Sylvius),    a 
deeper    part    of    the    Fissura 
lateralis  containing  the  Insula, 
rhoriiboidal,  the  floor  of  the  fourth 
ventricle,  118 
Fovea  limbica   (sulcus  rhinalis,  fis- 
sura rhinica,  fissura  rhinahs,  fis- 
sura    ectorhinahs),     the     sulcus 
which  marks  the  lateral  border  of 
the    lateral    Area    olfactoria   and 
Gyrus    hippocampi    or    pyriform 
Lobe  in  the  lower  mammals. 
Franz,  S.  I.,  299 
Freedom  of  action,  315 
Frey,  M.  von,  79,  84,  85,  94 
Fritsch,  G.,  281,  299 
Frog,  cerebral  cortex  of,  216,  264, 
279 
nerve  endings  in,  90,  92 
olfactory  receptors  in,  92 
reaction  time  of,  98 
reactions  of,  63 

velocity  of  nervous  transmission 
in,  97 
Funiculus,  one  of  the  three  principal 
divisions  of  white  matter  on 
each  side  of  the  spinal  cord; 
these  funiculi  were  formerly 
called  Columns,  128 
dorsal  (funiculus  dorsalis  or  pos- 
terior, posterior  columns),  the 
white  matter  of  the  spinal  cord 
included  between  tlae  dorsal 
fissure  and  the  dorsal  root,  128, 
130,  134,  138,  141,  150,  151, 
175,  176,  177,  178,  179,  310 


Funiculus,  lateral  (funiculus  later- 
alis, lateral  columns),  the  white 
matter  of  the  spinal  cord  in- 
cluded between  the  dorsal  and 
ventral  roots,  128 
ventral  (funiculus  ventralis  or  an- 
terior, ventral,  or  anterior  col- 
umns), the  white  matter  of  the 
spinal  cord  included  between  the 
ventral  fissure  and  the  ventral 
root,  128 


Gall,  F.  G.,  280,  281,  300 
Ganglion,  a  collection  of  nerve-cells. 

In  vertebrates  the  term  should  be 

apphed    only    to    peripheral    cell 

masses,  though  sometimes  Nuclei 

within  the  brain  are  so  designated, 

108,  109 
Ganglion  or  ganglia,  basal,  a  term 
sometimes  applied  to  the  Cor- 
pus striatum  and  other  sub- 
cortical parts  of  the  cerebral 
hemisphere. 

branchial,  of  vagus,  149 

cerebro-spinal,  development  of, 
45,  225 

cervical,  inferior,  226 
middle,  226 
superior,  226,  234 

ciliary,  143,  146,  149,  226,  231, 
246 

of  Corti.    See  Ganglion,  spiral. 

of  facial  nerve.  See  Ganglion, 
geniculate. 

Gasser's.  See  Ganglion,  semi- 
lunar. 

geniculate  (ganglion  geniculi,  the 
gangUon  of  the  VII  cranial  or 
facial  nerve).  111,  112,  146, 
149,  245,  256 

habenulse.     See  Habenula. 

of  insects,  29,  30 

interpedunculare.  See  Nucleus, 
interpeduncular. 

of  invertebrates,  28,  29,  30,  227 

jugular  (ganglion  jugulare),  147, 
149 

of  lateral  line  nerves,  149 

nodosum,  147,  237,  239,  240 

opticum  basale.  See  Nucleus, 
preoptic. 

otic,  147,  245 


INDEX    AND    GLOSSARY 


331 


Ganglion,  petrosal  (ganglion  petro- 
sum),  147,  245 
of  Scarpa.    See  Ganglion  vestibu- 
lar, 
semilunar     (ganglion    semilunare, 
Gasser's  ganglion,  the  ganglion 
of  the  V  cranial  or  trigeminal 
nerve),   45,   111,  112,  146,   ISO, 
245 
sphenopalatine,  226,  245 
spinal,  25,  43,  109,  125,  126,  134, 

135,  136,  141,  147,  227,  228 
spiral  (ganglion  spirale,  ganglion  of 

CORTI),  147 
submaxillary,  146 
superior  (ganglion  superius  of  IX 

cranial  nerve),  147 
supra-esophageal,  29,  30 
sympathetic,  53, 107, 109, 125, 126, 
225,  226,  227,  230,  237,  238, 
239 
prevertebral,  sympathetic  gan- 
glia of  the  thorax  and  abdo- 
men other  than  those  of  the 
sympathetic  trunk, 
vertebral,    the    ganglia    of    the 
sympathetic  Trunk, 
of     trigeminus.       See     Ganglion, 

semilunar, 
of  vagus.     See  GangUon,  jugular, 

and  Ganglion  nodosum, 
of  vertebrates,  108. 
vestibular   (ganglion  of  Scarpa), 
147 
Gehtjchten,  a.  van,  25,  45,  86,  194 
Generative  organs.     See  Sexual  or- 
gans. 
Geniculate  body.    See  Body,  genicu- 
late. 
ganglion.     See  Ganglion,   genicu- 
late. 
Gennari,   layer  of  stripe  of.     See 

Line  of  Gennari. 
Genu,    a   knee-shaped   bend   of   an 
organ,  such  as  the  genu  of  the 
corpus  callosum,   of  the  facial 
nerve,  etc. 
of  corpus  callosum,  119 
Gills,  236,  240 

innervation  of,  110,  111,  112,  149, 

245 
muscles  of,  94,  148 
Gland,  adrenal.     See  Gland,  supra- 
renal. 


Gland,  intestinal,  224 
nerve-endings  on,  94 
pineal.    See  Body,  pineal. 
pituitary.    See  Hypophysis. 
salivary,  innervation  of,  143,  144, 
146,    147,    154,    156,    232,  241, 
244 
suprarenal,  231,  255,  256 
Gha.     See  Neuroglia. 
Glomeruli,  olfactory,  small  globular 
masses  of  dense  Neuropil  in  the 
oKactory  bulb  containing  the  first 
synapse  in  the  olfactory  pathway, 
217,  218 
Glycosuria,  255 
Goldstein,  K.,  131,  194 
GoLGi,  C.,  41,  43,  44,  49,  55,  190, 

274 
GoLL,   column  of.     See  Fasciculus 

graciUs. 
GoLTZ,  F.,  279,  280,  281,  300 
GowERS,  fasciculus  of.    See  Fascic- 
ulus ventro-lateralis  superficialis. 
Gradient,    physiological,    in    nerve- 
fibers,  97 
Granules.     See  Cells,  granule. 

chromophilic,    tigroid,    of    NissL. 
See  Substance,  chromophihc. 
Gray,  central,  relatively  undifferen- 
tiated gray  Matter  which  retains 
its    primitive    position    near    the 
ventricles,  127. 
Groove,     medullary.      See    Neural 
groove. 
neural.    See  Neural  groove. 
Grijnbatjm,  a.  S.  F.,  282,  300 
GuDDEN,  commissure  of.    See  Com- 
missure, postoptic. 
Gustatory    apparatus,    72,    74,    91, 
143,  144,  146,  147,  148,  149,  150, 
157,  163,  218,  222,  234,  243-246, 
303 
Gyrus,  one  of  the  convolutions  or 
folds    of    the    cerebral    cortex 
bounded  by  Sulci  or  Fissures, 
265,  266 
angularis,  121 

centralis  anterior  (precentral  gy- 
rus), 121,  140,  181,  269,  271, 
272,  282,  283,  285,  286,  288 
posterior  (jiostcentral  gvrus), 
121,  268,  270,  282,  283',  285, 
286,  288 
cinguh,  119,  170 


332 


INDEX    AND    GLOSSARY 


Gyrus  dentatus  (fascia  dentata),  a 
subsidiary  gyrus  of  the  Hippo- 
campus, 221,  222 

fomicatus  (limbic  lobe),  the  mar- 
ginal portion  of  the  cerebral 
cortex  on  the  medial  aspect 
of  the  hemisphere,  including 
the  GjTTUs  cinguh.  Gyrus  hippo- 
campi, and  others;  there  is  a 
variety  of  usage  regarding  its 
limits,  273 

frontahs  inferior,  121,  170,  292 
medius,  121 
superior,  119,  121 

hippocampi,  that  part  of  the  cere- 
bral cortex  which  borders  the 
Hippocampus.  Part  of  it  (the 
Uncus)  is  Archipallium ;  the  re- 
mainder is  transitional  to  the 
Neopallium,  See  Lobe,  pyri- 
form,  217,  219,  221,  222,  273, 
284 

lingualis,  119 

occipitalis  lateralis,  121 

olfactorius  lateralis.    See  Nucleus 
olfactorius  lateralis, 
medialis.       See      Area     parol- 
factoria  of  Broca 

orbitalis,  121 

postcentral.  See  Gyrus  centralis 
posterior. 

precentral.  See  Gyrus  centralis 
anterior. 

subcallosus  (pedunculus  corporis 
callosi),  part  of  the  Nucleus  ol- 
factorius medialis,  119,  219 

supramarginalis,  121 

temporalis  inferior,  121 
medius,  121 
superior,  121,  170 

uncinatus.     See  Uncus. 


Habenula  (nucleus  habenulae,  gang- 
lion habenulse),  an  important  ol- 
factory correlation  center  in  the 
Epithalamus,  162,  165,  167,  170, 
220 

Habit,  physiological,  32,  294,  304 

Hair  cells  (cells  of  Corti),  197,  198, 
199 
innervation  of,  80,  81 

Hardesty,  I.,  198,  199,  203 

Harris,  W.,  213 


Head,  H.,  79,  84,  85,  94,  95,  132, 
142,  166,  171,  172,  173,  175,  179, 
233,  251,  253,  254,  262,  300,  311 
Hearing,  organs  of.     See  Auditory 

apparatus. 
Heart,  innervation  of,  144,  147,  232, 

234 
Heat,  sensations  of.     See  Tempera- 
ture, apparatus  of. 
Heidenhain,  M.,  49,  55 
Held,  H.,  50 
Helmholtz,    H.    L.   T.   von,   198, 

203 
Helwig,  tract  of.    See  Tract,  olivo- 
spinal. 
Hemispheres,  cerebellar,  120,  187 
cerebral,  63,  64,  111,  112, 121,  122, 
123,  129,  160,  215,  219,  264, 
265,  279 
comparative  anatomy  and  evo- 
lution of,  111,  112,  129,  215, 
264,  265,  279,  280,  290,  294, 
301-306 
Hemorrhage,  cerebral,  293 
Hensen,  cells  of,  197 
stripe  of,  197,  198 
Herrick,  C.  Judson,  36,  61,  66,  67, 
95,  124,  135,  142,  159,  171,  182, 
194,  200,  223,  248,  263,  303 
Herrick,  C.  L.,  18,  108,  194,  258, 

262,  296,  300,  303 
Herrick,  F.  H.,  61,  68 
Hertz,  A.  F.,  95,  242,  243,  248 
Hibernation,  nerve  cells  in,  102 
Hindbrain,  a  term  which  has  been 
variously  applied  to  the  cerebel- 
lum, the  cerebellum  and  pons,  the 
medulla  oblongata,  and  the  entire 
rhombencephalon. 
Hippocampal  gyrus.  ■  See  Gyrus  hip- 
pocampi. 
Hippocampus   (hippocampus  major, 
Ammon's   horn,  cornu   Ammo- 
nis) ,  a  submerged  gyrus  forming 
the  larger  part  of  the  Archipal- 
lium, or  olfactory  cerebral  cor- 
tex, 217,  219,  220,  221,  222,  273, 
284,  306 
commissure  of.      See  Commissure 

of  hippocampus, 
minor.     See  Calcar  avis. 
His,  William,  49,  55,  115-118,  124 
Histology,    the    study    of    Tissues, 
27 


INDEX    AND    GLOSSARY 


333 


HiTZiG,  E.,  281,  299,  300 

Hodge,  C.  F.,  105 

HoFEK,  B.,  199,  203 

Holmes,  G.,  16(3,  171,  254,  262,  280, 
300,  311 

Holmes,  S.  J.,  262 

Horn  (cornu),  one  of  the  three  chief 
parts  of  the  lateral  ventricle — 
anterior,  posterior,  and  inferior  or 
middle;  also  applied  to  the  gray 
Columns  of  the  spinal  cord. 

Hough,  Th.,  68 

HuBER,  G.  C.,  87,  95,  233 

Humor,  vitreous,  205 

Hunger,  apparatus  of,  89,  240 

Hyodon  tergissus,  brain  of,  302,  303 

Hypophysis  (pituitary  body,  pitui- 
tary gland),  a  glandular  appendage 
to  the  ventral  part  of  the  hypo- 
thalamus; its  posterior  lobe  is  an 
outgrowth  from  the  Neural  tube, 
its  anterior  lobe  is  an  ingrowth 
from  the  epithehiun  of  the  em- 
bryonic mouth  cavity,  114,  119, 
163,  167 

Hypothalamus,  the  ventral  subdivi- 
sion of  the  Diencephalon,  contain- 
ing the  Hypophysis  and  the  mam- 
mlllary  Body,  an  important  olfac- 
tory correlation  center,  117,  118, 
121,  122,  162,  163,  165,  166,  167, 
174,  176,  215,  220,  221,  222,  246, 
260 


Idiocy,  279,  290 

Imbecihty.     See  Idiocy. 

Impulse,  nervous,  nature  of,  96,  97 
velocity  of,  97,  98. 

Infundibulum,  a  funnel-shaped  ex- 
tension of  the  third  ventricle  pass- 
ing through  the  Hypothalamus  to 
the  end  in  the  Hypophysis,  114, 
119,  120,  163 

Inhibition,  the  diminution  or  arrest 
of  a  function,  63,  66,  108,  254, 
256,  279,  307 

Insanity,  290 

Insects,  nervous  system  of,  29,  30 
respiration  of,  236 

Instinct,  a  complex  form  of  in- 
variable Behavior,  32,  61,  257, 
263,  290,  301,  307,  309,  311,  312, 
313 


Insula  (island  of  Reil),  a  portion  of 
the  cerebral  cortex  which  is  sub- 
merged under  the  Fossa  lateraUs, 
166,  170,  266,  273 

Integration,  the  combination  of  dif- 
ferent acts  so  that  they  cooperate 
toward  a  common  end,  106 

Intelhgence.     See  Consciousness, 
lapsed,  32,  301,  309 

Interbrain.     See  Diencephalon. 

Interference  of  nervous  impulses,  58, 
61,  63,  307 

Interoceptor,  a  sense  organ  excited  by 
stimuh  arising  within  the  viscera; 
cf .  Visceral  apparatus  and  Visceral 
organs,  74,  77,  89,  243 

Intestines,  nerves  of,  144,  234,  241, 
242 

Intoxication,  effects  of,  97,  101,  102, 
103,  104,  231,  258 

Introspection,  98,  297,  309 

Intxunescentia  cervicaUs  (cervical 
enlargement),  the  enlargement 
of  the  spinal  cord  from  which 
the  nerves  of  the  arm  arise. 
lumbalis  (lumbar  enlargement), 
the  enlargement  of  the  spinal 
cord  from  which  the  nerves  of 
the  leg  arise. 

Invariable  behavior.  See  Behavior, 
invariable. 

Invertebrates,  behavior  of,  32 
nervous  system  of,  28 

Iris,  143,  211,  232,  234,  247 

Irradiation  of  nervous  impulses,  65, 
66,  100,  260,  268 

Island  of  Reil.     See  Insula. 

Isthmus,  a  narrow  segment  of  the 
brain  forming  the  upper  end  of  the 
Rhombencephalon  (B.  N.  A.);  it 
might  better  be  regarded  as 
merely  the  plane  of  separation  be- 
tween Rhombencephalon  and 
Cerebrum,  116-119,  121,  122,  143, 
160 

Iter  (iter  a  tertio  ad  quartum  ven- 
triculum).     See  Aqueduct  of  Syl- 


Jackson,  Hughlings,  292 
Jacobson,   nerve  of.      See    Nerve, 

tympanic. 
James,  W.,  259,  262 


334 


INDEX    AND    GLOSSARY 


Jelly-fishes,  nervous  system  of,  27, 

227 
Jennings,  H.  S.,  21,  31,  37,  68 
Johnston,  J.  B.,  124,  152,  159,  171, 

180,  223 
Joints,  nerve-endings  in,  88 


Kangaroo,  cerebral  cortex  of,  217 
Kappeks,  C.  U.  Akiens,  203,  223, 

240,  248,  265,  278,  310 
Kakplxjs,  J.  P.,  251,  262 
Karyoplasm,  the  protoplasm  of  the 

nucleus  of  a  cell,  96 
Keibel,  F.,  124 
kolliker,  a.,  44 
Krause,  W.,  115,  124 

end-bulbs  of,  84,  85 
Kreidl,  a.,  251,  262 

KrIES,  J.  VON,  71 

Ktjntz,  a.,  233 


Labium  vestibulare,  198 

Labyrinth  of  ear,  195,  196 

Lactic  acid,  103 

Ladd,  G.  T.,  98,  105,  213 

Lagena,  199,  200 

Lamina.     See  also  Layer.  - 

affixa,  a  thin  non-nervous  part  of 
the  medial  wall  of  the  cerebral 
hemisphere     attached     to     the 
thalamus  and  bordered  by  the 
lateral  chorioid  Plexus, 
of  neiu-al  tube.     See  Plate, 
terminalis    (terminal    plate),    the 
anterior  boundary  of  the  third 
ventricle,  118, 165,  215,  264,  265 
Lancisi  (Lancisius),  nerves  of.    See 
Stria  longitudinalis. 
stria?  of.    See  Stria  longitudinalis. 
Landacre,  F.  L.,  35 
Lange,  C,  259,  262 
Langley,  J.  N.,  148,  225,  229,  233 
Laqueus.     See  Lemniscus. 
Larynx,  239 
Lateral   line    organs.     See    Organs, 

lateral  line. 
Law,  myelogenetic,  of  Flechsig,  287 
Layer.     See  also  Lamina. 

of  Baillarger.     See  Line  of  Bail- 
larger, 
of  cerebellar  cortex,  190 
of  cerebral  cortex,  268-274,  290 


Layer  of  Gennari.      See   Line   of 
Gennari. 

of  retina,  205,  206,  207 
Learning.     See  Experience,  learning 

by. 
Lemniscus  (fillet,  laqueus),  sensory 
fibers  of  the  second  order  ter- 
minating in  the  thalamus. 

acoustic.     See  Lemniscus,  lateral. 

bulbar,  ascending  sensory  fibers  of 
the  second  order  from  the 
medulla  oblongata  to  the  thala- 
mus, including  several  different 
tracts,  157 

gustatory.  See  Lemniscus,  vis- 
ceral. 

lateral,  the  acoustic  lemniscus, 
fibers  from  the  cochlear  nuclei 
to  the  colhculus  inferior  and 
thalamus,  114,  157,  161,  163, 
164,  167,  174,  176,  185,  201 

medial,  ascending  fibers  of  the 
proprioceptive  system  from  the 
spinal  cord  to  the  thalamus,  138,\ 
141,  155, 156, 161, 163, 164, 165, 
167,  174,  175,  176, 177,  179,  180, 
210 

optic,  a  term  which  might  ap- 
propriately replace  optic  Tract, 
209 

spinal,  ascending  fibers  of  touch, 
temperature,  and  pain  sensibility 
from  the  spinal  cord  to  the 
thalamus.  In  the  cord  these 
fibers  form  two  tracts,  the  dor- 
sal and  ventral  spino-thalamic 
tracts,  130,  131,  134,  138,  139, 
141,  156,  161,  163,  164, 167,  173, 
174,  178,  179,  190,  252,  253 

trigeminal,  ascending  sensory 
fibers  of  the  second  order  from 
the  sensory  V  nuclei  to  the 
thalamus,  139,  141,  157,  161, 
163,  164,  165,  167,  173,  174,  180 

visceral,  a  name  suggested  for  the 
ascending  secondary  fibers  from 
the  nucleus  of  the  fasciculus  soli- 
tarius  to  the  higher  cerebral  cen- 
ters, 157,  246 
Lenhossek,  M.  von,  41 
Lens,  204-208,  211,  212 
Lewandowsky,  M.,  37,  194,  300 
Life,  definition  of,  17 
Ligament,  spiral,  of  Cochlea,  197 


INDEX    AND    GLOSSARY 


335 


Limbus  laminae  spiralis,  197 
Liinen  insukB.     See  Nucleus  olfac- 

torius  lateralis,  219 
Line  of  Baillarger,  a  stripe  of  tan- 
gential white  fibers  in  the  cere- 
bral cortex ;  there  is  an  outer  and 
an  inner  Une,  2G7,  268,  274 
of  Gennari,  a  stripe  of  tangential 
white  fibers  in  the  Area  striata 
of  the  cerebral  cortex;  it  is  the 
outer  Line  of  Baillarger  in  this 
area,  268,  274 
Lingula  cerebelli,  a  small  eminence 
on  the  ventral  surface  of  the  cere- 
bellum where  the  anterior  medul- 
lary   Velum    joins    the    Vermis, 
162 
LissAUER,   tract   of,    zone  gf.     See 

Fasciculus  dorso-laterahs. 
Lizard,  parietal  eye  of,  212 
Lobe,  frontal,  120,  266,  283 

of   the   lateral   line    (lobus   lineaj 
lateralis),  a  highly  differentiated 
part  of  the  acoustico-lateral  Area 
of  fishes,  152 
limbic.     See  Gyrus  fomicatus. 
occipital,  266,  283 
olfactory    (lobus  olfactorius),   the 
olfactory  Bulb,  its  Crus,  and  the 
anterior  part  of  the  Area  olfac- 
toria;  this  is  the  B.  N.  A.  usage; 
the  term  is  sometimes  applied  to 
the    olfactory   Bulb    alone   and 
sometimes   to   the  Area   olfac- 
toria  alone, 
optic.    See  Colliculus  superior. 
parietal,  266 

pyriform    (lobus    piriformis),    the 
lateral  exposed  portion  of  the 
olfactory     cerebral     cortex     in 
lower  mammals,   bounded  dor- 
sally  by  the  Fovea  limbica;  in 
man  it  is  represented   by   the 
Uncus  and  part  of  the  Gyrus 
hippocampi,  217 
temporal,  120,  201,  202,  219,  266 
vagal.    See  Lobe,  visceral, 
visceral    (lobus    visceralis,    vagal 
lobe,   lobus   vagi),   the  visceral 
sensory  Area  of  fishes,  148,  149, 
152,  153,  303 
Lobulus  paracentralis,  119 
parietalis  inferior,  121 
superior,  121 


Local  sign;  cf.  Localization  of  sensa- 
tion, 84,  229,  250,  259 
Localization  of  functions  in  central 
nervous  system,  65,  113,  230- 
232,  234,  280 
in  cerebellar  cortex,   189,  281, 

305 
in  cerebral  cortex,  189,  273,  280, 
281,  282,  283,  284-297,    305, 
307 
of  sensation,  79,  84,  85,  228-230, 
250,  259,  286 
Locomotion,  reflexes  of,  134 
LoEB,  J.,  37,  61,  68 
LowENTHAL,  tract  of.     See  Tract, 

tecto-spinal. 
LxjciANi,  L.,  194 
LUGAKO,  E.,  104 

Lumbricus,  nervous  system  of,  28 
Lungs,  innervation  of.    See  Respira- 
tory apparatus. 
LxTYS,  body  of.      See  body  of  Luys. 
Lyra.     See  Lyre  of  David. 
Lyre  of  David  (IjTa  Davidis,  psal- 
terium),  the  posterior  part  of  the 
Fornix  body,  including  the  Com- 
missura  hippocampi. 


Macula  sacculi,  196 
utricuU,  196 

Magendie,  foramen  of.  See  Fora- 
men of  Magendie. 

Mall,  F.  P.,  124 

Mammals,  cortical  regions  of,  273 

Mammillary  body.  See  Body,  mam- 
millary. 

Mantle.     See  Cortex,  cerebral. 

Marchi,  method  of,  48,  135 

Marie,  P.,  300 

Marsupial  animals,  cerebral  cortex 
of,  217 

Massa  intermedia  (commissura  mol- 
lis, soft  commissure,  middle  com- 
missure), a  band  of  gray  matter 
connecting  the  medial  surfaces  of 
the  two  thalami  across  the  third 
ventricle;  it  is  not  a  true  commis- 
sure, 119,  162 

Mast,  S.  O.,  213 

Mastication,  apparatus  of,  78,  143, 
146,  ISO,  244,  247 

Matter,  central  gray.  See  Gray, 
central. 


336 


INDEX    AND    GLOSSARY 


Matter,    gray    (substantia    grisea), 
gray  nervous  tissue   composed 
chiefly    of  nerve-cells   and  un- 
myelinated nerve-fibers,  108, 128 
white  (substantia  alba),  white  ner- 
vous tissue  composed  chiefly  of 
myelinated     nerve-fibers,     108, 
127,  128,  130 
Meatus,  external  auditory,  195 
Medial  (medialis),  nearer  the  median 

plane;  opposed  to  lateral. 
Median  (medianus),  lying  in  the  axis 
or  middle  plane  of  the  body  or  one 
of  its  members. 
Medius,  intermediate  between  two 

other  parts. 
Medulla  oblongata  (bulb),  the  Myel- 
encephalon  B.  N.  A. ;  the  older 
and  better  usage  includes  the 
whole  of  the  Rhombencephal- 
on except  the  Cerebellum  and 
Pons,  110,  111,  112,  116-120, 
121,  122,  143,  152,  154,  162, 
232,  244,  246,  302,  303 
reflexes  of,  143,  148,  181,  234, 
235,  302,  303 
spinalis.     See  Spinal  cord. 
Medullary     sheath.       See     Myelin 
sheath. 
tube.     See  Neural  tube. 
Meissner,  corpuscle  of,  82,  83 
plexus  of  (submucous  plexus),  53, 
241 
Membrane,  basilar,  of  spiral  organ, 
197,  198 
of  the  brain.     See  Meninges, 
hmiting,     of     retina     (membrana 
limitans  externa  and  interna), 
207 
mucous,  nerves  of,  90,  126,  146, 

215,  232 
nuclear,  99 

Schneiderian.    See  Epithelium,  ol- 
factory, 
tectorial',  197,  198,  199 
tympanic  (drum  membrane),  85, 

195,  196,  245,  249 
vestibular    (membrane   of  Reiss- 
ner),  197 
Memorv,  295,  297,  304,  307 

associative,  32,  65,  242,  294,  295, 
296,  307 
Menidia,  nerves  of,  148,  149,  200 
spinal  cord  of,  150 


Meninges,  the  membranes  of  the 
brain  and  spinal  cord,  38,  146,  250 

Merkel,  corpuscle  of,  81,  82,  83 

Mesencephalon  (midbrain),  the  Cor- 
pora quadrigemina  and  cerebral 
Peduncles,  62,  63,  116-119, 121, 
122,  160,  161,  232 
development  of,  116,  119,  160 

Metabolism,  chemical  changes  in 
protoplasm,  96,  97,  99,  163 

Metathalamus,  the  posterior  part  of 
the  Thalamus,  comprising  the  me- 
dial and  lateral  geniculate  Bodies, 
118,  121,  122,  163,  165,  167 

Metencephalon  (hindbrain),  the  an- 
terior part  of  the  Rhombenceph- 
alon, including  the  Cerebelliun, 
Pons,  and  intervening  part  of  the 
Medulla  oblongata,  117-119,  121 

Meyer,  A.,  49,  55,  293,  300 

Meyer,  Max,  262 

Meynert,  commissure  of.  See 
Commissure,  postoptic. 
decussation  of  (fountain  decussa- 
tion, dorsal  tegmental  decussa- 
tion), 161 
fasciculus  retroflexus  of.  See 
Tract,  habenulo-peduncular. 

Michelson,  a.  a.,  71 

Midbrain.     See  Mesencephalon. 

MiLLIKAN,  R.  A.,  71 

Mind.     See  Consciousness. 

evolution  of.     See  Psychogenesis. 
unconscious,  296,  297 

Molecular  substance.  Molecular 
layers,  a  name  appUed  to  the 
Neuropil. 

MOLHANT,   M.,   248 

MoNAKOW,  C.  VON,  171,  287,  293, 
294,  300 

tract  of.    See  Tract,  rubro-spinal. 
Monro,  foramen  of.     See  Foramen 

interventriculare. 
Moon-eye,  brain  of,  302,  303 
Morals,  313,  314,  315 
MoRGULis,  S.,  242,  248 
Motor  apparatus,  62,  63,  117,  120, 

154,  163,  180-182,  186,  192,  234, 

244,  246,  247,  261,  279,  309 
Moyes,  J.  M.,  278 
Mucous  membrane,  nerve  endings  in. 

See  Membrane,  mucous. 
Mi'LLER,  fibers  of,  205,  206 
Multiple  consciousness,  297 


INDEX    AND    GLOSSARY 


337 


MuNK,  H.,  300 
Muscarin,  231 

Muscle,     Muscles,    of    arm,    motor 
nuclei  of,  129 

cardiac,  the  muscle  of  the  heart,  a 
visceral  muscle  whose  fibers  are 
cross-striated,  93,  148,  224,  234 

of  eyeball.    See  Eye,  muscles  of. 

of  facial  expression,  innervation  of, 
144,  146,  244,  261 

intercostal,  innervation  of,  236- 
240 

involuntary,  muscles  not  under  di- 
rect control  of  the  will ;  they  are 
of  the  general  visceral  type,  93 

nerve  endings  in,  86,  87,  90,  92,  93 

respiratory,  236-239 

sense,  77,  87,  132,  141,  146,  172- 
180,  242 

skeletal.     See  Muscle,  somatic. 

smooth  or  unstriated,  visceral 
muscle  whose  fibers  are  not 
cross-striated,  87,  93,  147,  148 

somatic,  striated  muscles  derived 
from  the  Somites  of  the  embryo, 
skeletal  muscles,  87,  92,  145, 
147,  148 

spindle,  a  bundle  of  muscle-fibers, 
smaller  than  ordinary  fibers, 
which  are  supplied  with  special 
nerve  endings  of  the  muscle 
sense  in  addition  to  tjqDical 
motor  End-plates,  87 

sternocleidomastoid,  144,  147 

striated,  composed  of  fibers  hav- 
ing a  cross-striped  appearance; 
may  be  somatic  or  visceral,  87, 

92,  93 

synergic,  muscles  which  act  to- 
gether for  the  performance  of  a 
movement,  35,  306 

of  tongue.    See  Tongue,  muscles  of. 

trapezius,  innervation  of,  144,  147 

visceral,  unstriated  or  striated 
muscles  not  derived  from  the 
Somites  of  the  embryo;  may  be 
involuntary   or   voluntary,    87, 

93,  94,  126,  148,  224 
voluntary,    muscles    under    direct 

control    of    the    will;    may    be 
either  somatic  or  visceral,   92, 
93,94 
Mustelus,  nervous  system  of,   111, 
112 

22 


Mycetozoa,  22 

Myel  (myelon),  the  Spinal  cord. 

Myelencephalon  (afterbrain),  the 
posterior  part  of  the  Rhomben- 
cephalon, or  that  portion  of  the 
Medulla  oblongata  lying  behind 
the  Pons  and  Cerebellum,  117, 
118,  119,  121,  122 

Myelin,  a  fat-like  substance  formed  as 
a  sheath  around  the  myelinated 
(medullated)  nerve-fibers,  46 
sheath,  an  envelope  of  Myelin 
around  the  Axis-cylinder  of  some 
nerve-fibers,  40,  46,  108,  286 

Myelogeny,  the  sequence  of  matura- 
tion of  the  Myelin  sheaths  of 
nerve-fibers  in  the  development  of 
the  central  nervous  system,  286, 
287,  288 

Myelon  (myel),  the  Spinal  cord. 

Myotom.     See  Somites. 

Myxomycetes,  22 


Nates.     See  Colliculus  superior. 
Nausea,  apparatus  of,  89 
Necturus,  nervous  system  of,  62,  63 
Neencephalon,  the  new  brain,  i.  e., 
the  cerebral  cortex  and  its  depend- 
encies, 115,  263 
Negative  variation  in  nerve-fibers,  96 
Neopalliimi,  the  non-olfactory  part 
of  the  cerebral  cortex,  or  somatic 
cortex,  217,  220,  221 
Neothalamus    (new   thalamus),    the 
phylogenetically  new  part  of  the 
Thalamus,  which  is  a  cortical  de- 
pendency, 163-167,  263,  306 
Nerve  (nervns),  any  bundle  of  nerve- 
fibers  outside  the  central  ner- 
vous system,  28,  106 
abducens  (VI  cranial  nerve),  114, 
120,    143,    145,   146,    148,   150, 
180,  186 
accelerator,  of  heart,  234,  235 
accessory  (XI  cranial  nerve),  120, 

144,  145,  147,  148,  244 
acoustic  (Vm  cranial  nerve,  audi- 
tory  nerve,    nervus   acusticus), 
lid.  111,  112,  114,  120,  143,  145, 
147,  149, 183,  199,  200,  201 
afferent.     See  Afferent, 
anterior  cutaneous,  125 
auditory.     See  Nerve,  acoustic. 


338 


INDEX    AND    GLOSSARY 


Nerve,  auricular,  144,  147 

branchial,  110,  111,  112,  149,  245 

buccal,  200 

cardiac.     See  Heart,  innervation 

of. 
cerebral.     See  Nerve,  cranial, 
cerebro-spinal,      the      peripheral 
nerves  connected  with  the  brain 
and  spinal  cord,  107 
cervical,  107,  130,  237 
chorda  tympani,  146,  245 
ciliary,  146 
coccygeal,  107 
cochlear,  145,  157,  183,  185,  197, 

198,  200,  201 
components,  table  of,  146,  147 
cranial  (cerebral  nerve),  a  periph- 
eral nerve  connected  with  the 
brain;  these  nerves  are  enu- 
merated in  12  pairs,  106,  110, 
HI,   112,  143,   144-150,   152, 
154,  164 
of  fishes,  110,  111,  112,  148,  149 
cutaneous,  79-86,   125,   132,   134, 

143,  145-1.50,     157,     172-180, 
228,  245,  246,  252,  253 

of  Cyon,  235 

of  deep  sensibihty;  cf.  Proprio- 
ceptors, apparatus  of,  79,  86, 
132,  172-180 

depressor,  of  heart,  235 

efferent.     See  Efferent. 

excito-glandular,  108 

facial  (VII  cranial  nerve,  faciahs), 
110,  111,  112,  114,  120,  143,  145, 
146,  148,  150,  231,  236,  243, 
244, 245,  246 

glossopharyngeal  (IX  cranial 
nerve),  110,  111,  112,  114,  120, 

144,  145,  147,  148,  149, 150,  155, 
231,  243,  244,  245 

gustatory,  243-246 
hyomandibular,  110-112,  149 
hypoglossus   (XII  cranial  nerve), 

120,    144,    147,    148,    150,    153, 

156 
inhibitory,  a  nerve  which  checks 

or    retards    the    action    of    the 

organ   in   which   it   terminates, 

108,  234,  235 
intercostal,  125,  237,  238,  239 
intermediate  (nerve  of  Wrisberg, 

pars  intermedia  facialis,  portio 

intermedia  facialis,  the  smaller 


of    the    two    roots    of    the    VII 

cranial  nerve),  114,  120,  146,  244, 

245 
Nerve,  intestinal.  111,  149 

of  Jacobson.  See  Nerve,  tym- 
panic. 

of  Lancisi.  See  Stria  longitudi- 
nalis. 

laryngeal,  147 

lateral  (nervus  lateraUs,  lateral 
hne  nerves),  branches  of  the 
VII,  IX,  and  X  cranial  nerves 
which  supply  the  Lateral  line 
organs,  110,  111,  112,  145, 
148,  149,  152,  199,  200 
accessory    (ramus   lateralis    ac- 

cessorius  faciahs),  149,  246 
cutaneous,  125 

hngual,  147,  245 

lumbar,  107,  130,  231,  232 

mandibular,  110,  111,  146,  200,  245 

maxillary,  110,  111,  146,  226,  245 

motor,  a  peripheral  nerve  which 
conducts  efferent  impulses  to  a 
muscle,  108,  120,  14&-150 

oculomotor  (III  cranial  nerve), 
114,  120,  143,  145,  146,  148,  149, 
150,  160,  161,  ISO,  186,  210,  231, 
246 

olfactory  (nervus  olfactorius,  the 
first  cranial  nerve),  91,  110,  111, 
112,  143,  146,  148,  149,  150,  160, 
200,  215,  216,  217,  264 

ophthalmic,  110,  111,  146,  149, 
200,  245 

optic  (nervus  opticus,  the  second 
cranial  nerve) ;  this  is  not  a  true 
nerve,  but,  in  reality,  a  cerebral 
tract;  cf.  Tract,  optic,  111,  120, 
123,  143,  145,  146,  149,  165,  200, 
204,  205,  208,  209 

otic,  149 

of  pain,  249,  251,  252,  253,  254, 
257,  258 

palatine,  a  nerve  of  fishes  corre- 
sponding to  the  hiiman  great 
superficial  petrosal  nerve,  110, 
111,  112,  149 

parietal  (nerve  of  the  Parietal 
eye),  212 

phrenic,  236,  237,  238,  239 

pneumogastric.    See  Nerve,  vagus. 

postganglionic.  See  Neuron,  post- 
ganglionic. 


INDEX    AND    GLOSSARY 


339 


Nerve,  preganglionic.     See  Neuron, 
preganglionic. 

prespirat'ulur  (prctrematic  branch 
of  the  facial),  111,  149 

prctrematic,  of  facial,  111,  149 

recurrent,  226 

sacral,  107,  130,  231,  232 

sciatic,  97 

sensory,  a  peripheral  nerve  which 
conducts  afferent  impulses  from 
a  sense  organ  to  the  spinal  cord 
or  brain,  108,  12G 

somatic,  126,  139,  145,  172 

spinal,  a  peripheral  nerve  con- 
nected with  the  spinal  cord, 
lOG,  107,  114,  125,  126,  252 
central  connections  of,  129-140, 
150,  151,  251,  252,  253,  254 
components  of,  145,  147,  150, 
151 

splanchnic,  226 

superficial  petrosal,  147,  245 

supratemporal,  149 

sympathetic.  See  Nervous  sys- 
tem, sympathetic. 

of  taste.  See  Gustatory  appara- 
tus. 

terminal,  a  slender  nerve  associ- 
ated with  the  oKactory  nerve, 
111,  147,  215 

thoracic,  107,  125,  126,  130,  231, 
232,  236,  237 

trigeminal  (trifacial  nerve,  V 
cranial  nerve),  110,  111,  114, 
120,    141,    143,    145,    146,    148, 

149,  150,    152,    154,    157,    174, 

150,  243,  244,  245 

trochlear  (patheticus,  VI  cranial 
nerve),  110,  114,  120,  143,  145, 

146,  148,  150,  154,  160,  162,  ISO, 
186 

tympanic    (nerve    of    Jacobson), 

147,  245 

vagus  (pneumogastric  nerve,  X 
cranial  nerve),  110,  111,  112, 
114,  120,  144,  145,  147,  148,  150, 
152,  153,  156,  226,  231,  234-245 

vasoconstrictor,  235 

vasodilator,  235 

vasomotor.  See  Vasomotor  ap- 
paratus. 

vestibular,  88,  110,  111,  145,  147, 
176,  1S3,  184,  185, 187,  188,  198, 
200,  201 


Nerve,  vidian,  245 

visceral,  126,  144,  145-150,  259 
of  Wrisbekg.     See  Nerve,  inter- 
mediate. 
Nerve-cell.     See  Neuron. 
Nerve-fiber,  a  slender  fibrous  proc- 
ess of  a  Neuron,  39 
afferent,  lOS 

carbon  dioxid  production  in,  96,  97 
conduction  in,  96,  97 
degeneration  of,  46 
efferent;  cf.  also  Efferent,  108 
electric  changes  in,  96 
fatigue  of,  96,  101 
meduUated.  See  Nerve-fiber,  mye- 
linated, 
myelinated,  a  fiber  i:)rovitled  with 

a  MyeUn  sheath,  97,  108,  286 
postganglionic.    See  Neuron,  post- 
ganglionic. 
preganglionic.     See  Neuron,  pre- 
ganglionic. 
rate  of  transmission  in,  97,  98 
regeneration  of,  46 
unmyelinated  or  unmeduUated,  a 
fiber  devoid  of  a  MyeUn  sheath, 
108 
Nervous  impulse,  nature  of,  96,  97 

velocity  of,  97,  98 
Nervous  system,  the  aggregate  of  aU 
nervous  tissues, 
autonomic;  cf.  Nervous  system, 

sympathetic,  225,  229 
central,  28,  106,  107 
cerebro-spmal,  76,  225 
development  of,  106,  115,  116, 
117,  118,  120,  123,  153,  181, 
182,  204,  219,  264,  286,  290 
diffuse,  27,  53,  66,  227,  251 
embryonic.     See  Nervous  sys- 
tem, development  of. 
evolution  of;   see  also  Cortex, 
cerebral,    evolution    of,    and 
Hemisphere,    cerebral,    com- 
parative anatomy  and  evolu- 
tion of,  22,  24,  27,  33,  34,  113, 
115,  129,  ISO,  181,  182,  212, 
215,  219,  227,  251,  2.52,  253, 
263,  280,  294,  301,  306 
general  anatomy  of,  106 

cerebro-spinal  visceral,  227 
invertebrate,  27,  53,  227 
nomenclature  of,  115,  121.  122, 
123,  127,  128 


340 


INDEX    AND    GLOSSARY 


Nervous  system,  peripheral,  106 
phylogeny  of.    See  Nervous  sys- 
tem, evolution  of. 
physiology  of,  96 
segmental.      See    Segmentation 

and  Segmental  apparatus, 
subdivision  of,  106,  115-123 
sympathetic,  53,  65,  76,  89,  93, 
106,  107,  125,  126, 147,  148, 
150,  211,  224-233,  234,  241, 
242,  255,  259 
peripheral  autonomous  part, 
225,  227 
synaptic,  53 
vertebrate,  29,  106 
Neural  canal.    See  Canal,  neural, 
groove     (medullary    groove),    the 
trough-like  form  assumed  by  the 
Neural    plate    during    its    in- 
vagination to  form  the  Neural 
tube, 
plate,  a  thickened  plate  of  Ecto- 
derm in  early  vertebrate  em- 
bryos from  which  the  Neural 
tube  develops. 
tube,  the  embryonic  central  ner- 
vous system  when  in  the  form 
of  an  epithelial  tube,  106,  116, 
126,  160,  181 
Neurasthenia,  103 
Neuraxis,  the  central  nervous  sys- 
tem;    and    also    applied    to    the 
Axon. 
Neuraxon.     See  Axon. 
Neurenteric  canal,  in  the  embryo,  a 
communication       between       the 
caudal  end  of  the  Neural  tube  and 
the  digestive  tract. 
Neurilemma,  the  outer  sheath  of  a 

peripheral  nerve-fiber,  40,  46 
Nemite.     See  Axon. 
Neuroblast,  an  immature  nerve  cell, 

39,  45 
Neurocyte.     See  Neuron. 
Neurofibrils,    delicate    protoplasmic 
fibrils  within  the  cytoplasm  of  the 
Neuron,  40,  46,  47,  102 
Neuroglia  (glia),  a  supporting  fabric 
of  cells  and  horny  fibers  pervad- 
ing the  central  nervous  system,  38, 
104,  190,  205,  206,  269 
Neurogram,  295 

Neuromasts.      See    Organs,   lateral 
line. 


Neuromere,  one  of  the  segments  of 

the  embryonic  Neural  tube. 
Nexu"on    (neurocyte),    a  nerve   cell; 
cf.  Cell,  38,  40,  41, 42,  49,  56,  96, 
190,  268,  269,  270,  274 
afferent,  42 
bipolar,  44,  45 
correlation,  133,  134,  158 
efferent,  42 

fatigue  of,  96,  101,  102 
of  first,  second,  etc.,  order,  42 
multiform.      See    Neuron,    poly- 
morphic, 
polarization  of.     See  Polarity  of 

the  Neuron, 
polymorphic,  268,  269,  274 
postganglionic,   an   efferent   sym- 
pathetic   neuron   which    is   ex- 
cited by  a  preganglionic  Neuron, 
94,  126,  146,  147,  229,  231,  235, 
238,  239.  244 
preganglionic,  an  efferent  sympa- 
thetic neuron  whose  cell  body 
Ues  in  the  central  nervous  sys- 
tem, 93,  126,  146-148,  150,  229, 
231,  234,  235,  238,  239,  241,  244 
pyramidal,  of  cerebral  cortex,  42, 

44,  269,  270,  274,  290 
retraction  of,  103 
type  I,  43,  44,  190 
type  II,  43,  44,  190,  268,  269 
unipolar,  45 
Neurone.     See  Neuron. 
Neuropil  (molecular  substance,  dot- 
ted substance),   an  entanglement 
of  unmyehnated  fibers  containing 
many  synapses,  65 
Neuropore,  in  the  embryonic  brain 
an  opening  between  the  anterior 
end  of  the  neural  Canal  and  the 
exterior,  116 
Nicotin,  231 

Nidulus.     See  Nucleus  (2). 
Nidus,  a  depression  on  the  ventral 
surface    of    the    cerebellum;    also 
used  as  a  synonym  for  Nucleus 
(2),  108 
NissL,  F.,  42,  46,  55,  274 

bodies  of,  granules  of,  substance 
of.     See     Substance,     chromo- 
philic. 
Nociceptor,  a  sense  organ  or  Recep- 
tor which  responds   to  injurious 
influences. 


INDEX    AND    GLOSSARY 


341 


Node  of  Ranvier,  an  interruption  of 
the  Myelin  sheath  of  a  nerve-fiber, 
40 
Node,  vital,  240 

Nomenclature.      See    Nervous    sys- 
tem, nomenclature  of. 
Nose.    See  Olfactory  apparatus. 
Nose  brain   (Rhinencephalon) ,   112, 

123 
Nucleus  (1),  the  differentiated  cen- 
tral protoplasm  of  a  cell,  39,  40, 
41,  42,  47,  96,  99,  102,  108 
Nucleus  (2),  a  group  of  nerve-ceUs 
within  the  central  nervous  sys- 
tem;  also   called    Nidulus   and 
Nidus;  cf.  Ganglion,  108. 
of  abducens  nerve,  60,  146,  150, 

154,  185,  201 
acoustic.    See  Nucleus,  cochlear, 
ambiguus,  147,  150,  153,  154,  155, 

156,  185,  244 
amygdalae  (amygdala),  a  small 
mass  of  subcortical  gray  matter 
under  the  tip  of  the  temporal 
lobe  which  forms  part  of  the 
Nucleus  olfactorius  lateralis, 
144,  166,  273 
anterior    thalami,    164-166,    167, 

220 
arcuate,  155 

of  auditory  nerve.     See  Nucleus, 
cochlear,  and  Nucleus,  vestibu- 
lar, 
of   Bechterew,   vestibular,    184, 

185 
caudate    (nucleus   caudatus),    one 
of  the  two  large  gray  masses  of 
the  Corpus  striatum,  114,  162, 
166,  169,  170,  222 
of  Clarke.     See  Nucleus,  dorsal, 

of  Clarke. 
cochlear,   60,   63,    150,    154,   157, 

164,  185,  201 
commissural,  of  Cajal,  154,  164, 

240,  244,  247 
of  Deiters,  vestibular,  184,  185 
dentate,  a  large  nucleus  embedded 
within  the  cerebellar  hemisphere 
from   which    the   fibers   of   the 
Brachium    conjunctivum    arise, 
114,  188,  190,  191,  201 
dorsal,    of    Clarke    (nucleus    dor- 
salis   of   Clarke    or   Stilling, 
Clarke's   column),    a   longitu- 


dinal strand  of  neurones   of  the 

spinal   cord    whose   axones   enter 

the    spino-cerebellar    tracts,    130. 

137,  139,  176 
Nucleus   of  dorsal    funiculus.      See 
Clava  and    Tuberculiun   cune- 
atum. 

dorsal,  of  vagus.  See  Nucleus  of 
vagus,  dorsal. 

dorsalis  thalami.  See  Nucleus 
anterior  thalami. 

dorso-lateral,  of  spinal  cord,  a  col- 
lection of  neurones  in  the  ven- 
tral gray  column  which  inner- 
vate the  muscles  of  the  Umbs, 
129, 130 

of  Edinger-Westphal,  the  visceral 
efferent  nucleus  of  the  oculo- 
motor nerve,  146,  150,  154,  246 

emboliformis,  191,  201 

of  facial  nerve,  146,  150,  154,  244 

of  fasciculus  cuneatus.  See  Tu- 
berculum  cuneatum. 

of  fasciculus  gracilis.    See  Clava. 

of  fasciculus  solitarius,  the  visceral 
sensory  nucleus  of  the  VII,  IX, 
and  X  cranial  nerves,  150,  154, 
155,  156,  234,  237,  239, 240,  243, 
246,  247 

fastigii,  191,  201 

globosus,  191 

of  glossopharyngeus  nerve,  150 

habenulse.     See  Habenula. 

of  hypoglossus  nerve,  147,  150, 
154,  156 

interpeduncular,  a  nucleus  lying 
between  the  cerebral  peduncles 
which  receives  the  habenulo- 
peduncular  tract. 

of  lateral  lemniscus,  185,  201 

lateralis  thalami,  163,  164-166,167, 
170,  174,  176,  177,  253,  285,  306 

lattice,  of  thalamus.  See  Nucleus 
reticularis  thalami. 

lentiform  (nucleus  lentiformis,  len- 
ticular nucleus),  one  of  the  two 
large  gray  masses  of  the  Corpus 
striatum,"  114,  166,  169,  170 

magnoccUularis  tecti.  See  Nucleus, 
mesencephalic,  of  V  nerve. 

masticatory.  See  Nucleus  of 
trigeminus,  motor. 

medialis  thalami,  163,  164,  166, 
167,  170,  174,  176,  306 


342 


INDEX    AND    GLOSSARY 


Nucleus,  mesencephalic,  of  V  nerve, 
146,  154,  161,  164,  180 
motorius  tegmenti,  181 
of  oculomotor  nerve,  62,  63,  64, 
146,  150,  154, 160,  161,  185,  211, 
246 
olfactorius  anterior,  the  anterior 
undifferentiated     portion     of 
the  Area  olfactoria,  220 
intermedius.     See  Tuberculum 

olfactorium. 
lateralis,  the  lateral  portion  of 
the  Area  olfactoria,  lying  be- 
tween the  olfactory  Bulb  and 
the  Uncus,  219 
medialis,  the  medial  portion  of 
the  Area  olfactoria,  contain- 
ing  the   Septum  and   Gyrus 
subcallosus,  219 
oHvary.     See  Olive, 
of  origin,  108,  128 
pontile  (pontile  nuclei,  nuclei  pon- 

tis),  158,  187,  188,  289 
posterior  thalami,  163,   164,  165, 

167  _ 
preoptic    (ganglion    opticum    ba- 

sale),  220 
reticularis  thalami  (lattice  nucleus, 

Gitterschicht),  306 
roof,    of    cerebellum    (nuclei    fas- 
tigii,    globosus,  and    embolifor- 
mis),  188,  191 
ruber  (red  nucleus),  158,  161,  166, 

188,  189,  210,  289 
salivatory,  146,  147,  154,  156,  241, 

244,  247 
of  ScHWALBE,  vestibular,  184,  185 
of  Stilling.    See  Nucleus,  dorsal, 

of  Clarke. 
terminal,  108,  112 
of  trigeminus,  chief  sensory,  149, 
154,  157,  164,  174,  180,  244 
motor,  146,  150,  154,  180,  244 
spinal     (nucleus    of    spinal    V 
tract ;  old  term,  gelatinous  sub- 
stance of  Rolando  of  medulla 
oblongata),  149,  154, 155, 156, 
157,  164,  174,  180,  244 
of  trochlear  nerve,  146,  150,  154, 

160,  185,201,211 
of  vagus,   dorsal,    147,    150,    154, 
155,  156,  234,  237,  238,  239,  244 
of  ventral  gray  column  of  spinal 
cord,  129,  130 


Nucleus,  ventralis  thalami,  163,  164, 
165,  166,  167,  174,  176,  177,  253, 
285,  306 
ventro-lateral,  of    spinal    cord,    a 
collection    of    neurones    in    the 
ventral  gray  column  which  in- 
nervate   the    muscles    of    the 
limbs,  129,  130 
ventro-medialj  of  the  spinal  cord, 
a  collection  of  neurones  in  the 
ventral  gray  column  which  in- 
nervate   the    muscles    of    the 
trunk. 
vestibular,  143,  150,  154,  155,  156, 
164,  176,  184,  185,  186,  201 
NuEL,  J.  P.,  214 

space  of,  197 
Number  of  Betz  cells,  284 

of  fibers  in  human  pyramidal  tract, 

284 
of  neurones  in  cerebral  cortex,  26 


Obersteiner,  H.,  269 
Oblongata.     See  Medulla  oblongata. 
Olfactory  apparatus.    See  also  Rhi- 
nencephalon,  72,  74,  86,  91,  92, 110, 
111,  112,  122,  146,  148,  160,  162, 
163,  215-223,  273,  279 
Olive,  accessory,  155 

inferior    (oliva,    nucleus    olivaris, 
olivary  body),  a  large  gray  cen- 
ter  in   the   medulla   oblongata 
which  produces  an  eminence  on 
its  lateral  surface,  114,  131,  155, 
156,  158,  174,  188 
superior,  a  nucleus  in  the  second- 
ary auditory  path  embedded 
in  the  medulla  oblongata  dor- 
sally  of  the  pons,  60,  164,  185, 
201 
peduncle  of,  201 
Onuf,  B.,  233 

Operculum,  the  lobules  of  the  fron- 
tal, parietal,   and  temporal  cere- 
bral cortex  which  cover  the  Insula, 
121,  170,  266 
Ophthalmencephalon,  the  retina,  op- 
tic nerve,  and  visual  apparatus  of 
the  brain. 
Opossum,  cerebral  cortex  of,  217 
Optic    apparatus.      See   Visual   ap- 
paratus, 
chiasma.    See  Chiasma,  optic. 


INDEX    AND    GLOSSARY 


343 


Oj)tic  tectum,  an  optic  reflex  center 
in  the  roof  of  the  midbrain.     Sec 
CoUiculus,  superior, 
thalamus.    See  Diencephalon. 
vesicle.     See  Vesicle,  optic. 
Oral,  pertaining  to  the  mouth,   or 
directed  toward  the  mouth,  as 
opposed  to  Caudal. 
sense  of  Edinger,  219 
Organ  (organon),  a  part  of  the  body 
with  a  particular  function,  24 
of  CoRTi.    See  Organ,  spiral, 
generative.    See  sexual  organs. 
lateral    line    (neuromasts),    sense 
organs  in  or  under  the  skin  of 
fishes    and    amphibians    of    in- 
termediate   type   between   tac- 
tile and  auditory  organs,  110- 
112,    145,    148,   149,    152,    199, 
200 
parietal.     See  Parietal  eye. 
pineal.     See  Body,  pineal, 
spiral  (organon  spirale),  the  organ 
of  CoRTi  or  receptor  for  sound  in 
the  Cochlea,  85,  197,  198,  199 
Ossicles,  auditory,  195,  196 
Oxydation  in  neurones,  96,  97,  99 
Oxygen  as  respiratory  stimulus,  238 


Pacinian  corpuscle,  79,  80,  88 

Pain,  apparatus  of;  cf.  Affection,  85, 

89,  131,  132,  137,  138,  139,  141, 

163-167, 172-174,  178-180,  228- 

230,  243,  249-262,  286 

conduction   paths   for,    249,    251, 

252,  253,  254,  257,  258 
referred,  228,  229,  230,  261 
thalamic  center  for.    See  Thala- 
mus, pain  center  in. 
Palaeencephalon,  the  old  brain,  i.  c, 
all  of  the  brain  except  the  cerebral 
cortex  and  its  dependencies,  115, 
363 
Palasothalamus  (old   thalanuis),  the 
pliylogcnotically   old    part   of   the 
Thalamus,     present     in     animals 
which  lack  the  cerebral  cortex,  163, 
166 
Palate,  243 

PaUium.     See  Cortex,  cerebral,  216 
Pancreas,  224 

Paralysis  from   central  lesion,   173, 
178,  292 


Paraphysis,  an  cvagination  of  the 
membranous  roof  of  the  telen- 
cephalon in  front  of  the  Velum 
transversum  in  some  vertebrate 
brains. 
Parietal  eye  (parietal  organ,  ])ineal 
eye,  epiphyseal  ej^e),  a  modifica- 
tion of  the  pineal  Body  in  some 
lower  vertebrates  to  form  a  dorsal 
median  eye,  162,  212 
Parker,  G.  H.,  37,  75,  95,  199,  203, 

212,  214 
Parmelee,  M.,  37 
Pars  intermedia  of  Wrisberg.     See 

Nerve,  intermediate. 
Pars    mamillaris    hypothabni,    the 
mammillary    bodies    and    their 
envu'ons,  118 
optica     hypothalami,     the     optic 
Chiasma  and  its  environs,  118, 
121,  122 
Pause,  central,  98 
Pawlow^  I.,  242,  248 
Pedagogy.     See  Education. 
Peduncle   (pedunculus),  a  peduncle 
or  stalk.     See  Crus. 
cerebellar,  one  of  the  fibrous  stalks 
by  which  the  cerebellum  is  at- 
tached to  the  brain  stem.    There 
are  three  peduncles  on  each  side: 
(1)  the  superior  peduncle  (Bra- 
chium   conjunctivum) ,    (2)    the 
middle  peduncle  (Brachium  pon- 
tis),    (3)    the   inferior   peduncle 
(Corpus  restiforme),   158,    187, 
188 
cerebral  (pedunculus  cerebri),  the 
ventral    part    of    the    mesen- 
cephalon,   118,    119,    120,    121, 
158,  160,  167,  210,  211,  306 
of   corpus   callosum.     See   Gyrus 

subcallosus. 
of  superior  olive,  201 
Perikaryon,     the    protoplasm     sur- 
rounding   the    nucleus    in    the 
Cell  body  of  a  Neuron. 
functions  of,  99 
Perilymph,  196 

Perineureum,  the   connective-tissue 
sheath    surroimding   a    pei'iplu^ral 
nerve     . 
P(^i-istalsis,  241 
Peritoneum,  80,  250 
Pes  pediniculi.    See  Basis  pedunculi. 


344 


INDEX   AND    GLOSSARY 


Pharynx,  innervation  of,   144,   147, 

243 
Philippson,  M.,  133,  135,  142 
Photoreceptors,  nervous  End-organs 

sensitive  to  hght,  212 
Phrenology,  280,  281,  285 
Phylogeny  of  nervous  system.     See 

Nervous  system,  evolution  of. 
Physiognomy,  280 
Pia  mateJ:,  the  inner  brain  membrane. 
Pigment,  retinal.     See  Retina,  pig- 
ment of. 
Pike,  F.  H.,  194 
Pillar  of  CoRTi,  197,  198 

of  fornix.    See  Fornix  column  and 
Fornix  crus. 
Pilocarpin,  231 
Pineal  body.    See  Body,  pineal. 

eye.    See  Parietal  eye. 
Pituitary  body.    See  Hypophysis. 
Plants  contrasted  with  animals,  22 
Plasticity  in  behavior.   See  Behavior, 

variable. 
Plate   (lamina),  a  general  term  ap- 
pHed  to  any  flat  structure  or 
layer;    specifically    to    the    six 
longitudinal  bands  or  zones  into 
which  the  Neural  tube  is  divided 
as  explained   in    the   following 
definitions,  117. 
dorsal  (roof  plate,  Deckplatte) ,  the 
unpaired     dorsal     longitudinal 
epithelial   zone   of   the   Neural 
tube;  it  is  non-nervous  and  in 
some  parts  of  the  adult  brain  is 
enlarged  to  form  a  Tela,  153. 
dorso-lateral     (alar    plate,     wing 
plate,  epencephahc  region,  Flii- 
gelplatte),    one    of    a    pair    of 
dorso-lateral  longitudinal  zones 
of  the  Neural  tube ;  it  gives  rise 
to  the  dorsal  gray  column  of  the 
spinal  cord  and  to  the  sensory 
centers  of  the  brain,  117,  120, 
153 
floor.     See  Plate,  ventral, 
neural.     See  Neural  plate, 
roof.     See  Plate,  dorsal, 
ventral  (floor  plate,  Bodenplatte), 
the    unpaired    ventral    longitu- 
dinal zone  of  the  Neural  tube; 
it  is  originally  non-nervous,  but 
in  the  adult  is  invaded  by  the 
ventral  Commissixre,  153 


Plate,  ventro-lateral  (basal  plate, 
hypencephahc  region,  Boden- 
platte), one  of  a  pair  of  ventro- 
lateral longitudinal  zones  of  the 
Neural  tube;  it  gives  rise  to  the 
ventral  gray  column  of  the  cord 
and  to  the  motor  centers  of  the 
brain,  117,  120,  153 
Play,  257 

Pleasantness,   Pleasure.     See  Affec- 
tion. 
Pleura,  125,  250 

Plexus,    chorioid    (choroid    plexus, 
plexus    chorioideus),    a    thin 
non-nervous    portion   of    the- 
brain  waU   to  which   highly 
vascular  Pia  mater  is  adherent 
and  which  is  crumpled  and 
thrust    into    the    brain   ven- 
tricles. 
lateral,  the  chorioid  plexuses  of 
the  lateral  ventricles  of  the 
cerebral  hemispheres,  222 
of  fourth  ventricle  (plexus  cho- 
rioideus ventriculi  quarti) ,  the 
chorioid  plexus  which  forms 
the  roof  of  the  fourth  ven- 
tricle, 119,  121,  152,  264 
of  third  ventricle  (plexus  chori- 
oideus ventriculi  tertii),   the 
chorioid  plexus  which  forms 
the   roof   of   the   third   ven- 
tricle, 162,  166,  167 
ganglionic,  of  sympathetic  nervous 
system,    an    entanglement    of 
sympathetic  nerves  and  ganghon 
cells;  most  of  the  nervous  plex- 
uses enumerated  in  the  follow- 
ing list  are  ganglionic  plexuses 
of  this  type,  225,  226,  241 
nervous,  an  interlacing  of  differ- 
ent kinds  of  nerve-fibers,  53 
aortic,  226 
of  AxjERBACH  (myenteric  plexus), 

241 
brachial,  226 
bronchial,  226,238 
cardiac,  226,  235 
cehac,  226 
cervical,  226 
coronary,  226 
esophageal,  226 
gastric,  226 
hypogastric,  226,  239 


INDEX    AND    GLOSSARY 


345 


Plexus,  nervous,  lumbar,  226 

of  Meissner  (submucous  plex- 
us), 53,  241 
mesenteric,  226 
myenteric     (plexus    of    Auer- 

bach),  241 
pelvic,  226 
pharyngeal,  226 
sacral,  226 

solar.     See  Plexus,  celiac. 
submucous    (plexus   of    Meiss- 

nee),  53,  241 
vesical,  226 
Poisons,    susceptibility   of  neurones 

to,  97,  101-104,  231,  258 
Polarity  of  the  neuron,  39,  52,  97 
POLIMANTI,  O.,  135,  142 
Pons   (pons  Varolii),  a  projection 
from  the  under  surface  of  the 
medulla    oblongata    below    the 
cerebellum,  114,    118-120,    121, 
122,    143,    154,   158,    187,    188, 
220 
nuclei  of.     See  Nucleus,  pontile. 
Portio    dura   facialis    (motor   facial 
root),  146 
intermedia.     See  Nerve,  interme- 
diate, 
major  trigemini  (sensory  root  of 

the  trigeminus),  146 
minor  trigemini  (motor  root  of  the 
trigeminus),  146 
Posterior,  as  used  in  this  work  means 
toward  the  tail  end  of  the  body ;  as 
used   in   the   B.  N.  A.  tables   it 
means  toward  the  dorsal  side,  115, 
116 
Posture,  apparatus  of,  77,  89,  130, 

137,  254 
Precuneus,  119 

Prentiss,  C.  W.,  198,  199,  203 
Pressure,  apparatus  of.    See  Touch, 

apparatus  of. 
Primitive  sheath.    See  Neurilemma. 
Prince,  Morton,  295,  297,  300 
Prionotus  carolinus,  nervous  system 

of,  151,  153 
Process,  axis-cylinder.     See  Axon. 
ciliary,  of  eyeball,  143,  146,  232, 

247 
protoplasmic.     See  Dendrite. 
Processus  reticularis,  the  Formatio 
reticularis  of  the  spinal  cord,  127, 
129 


Projection  centers,  those  parts  of  the 
cerebral  cortex  which  receive  or 
give  rise  to  Projection  fibers ;  cf . 
Center,  cortical,  166,  273,  282, 
283,  284-289,  292,  306 
fibers,   fibers  which   connect   the 
cerebral  cortex  with  the  brain 
stem,   164,  165,   166,  167,   168, 
221,   266,   268,   269,  271,  284- 
287,  289 
Proprioceptor,  a  sense  organ  lying 
within  the  deep  tissues  of  the 
body    for    the    coordination    of 
somatic  reactions,  77,  86 
apparatus  of,  130,  132,  137,  138, 
139, 141, 145,  163-167, 172, 175- 
179,  2.54,  286 
Prosencephalon  (forebrain),  the  Di- 
encephalon    and    Telencephalon; 
sometimes  applied  to  the  Cerebral 
hemispheres  only,   117-119,  121, 
160 
Protista,  22 

Protopathic  sensibility,  a  primitive 
type   of  diffuse   cutaneous   sensi- 
bility,    especially     on     hair-clad 
parts,  84,  85,  132 
Protoplasm,  hving  substance,  24,  69, 
96 
nervous,  38,  69,  96 
Protozoa,  one-celled  animals,  24,  314 
Psalterium.    See  Lyre  of  David. 
Pseudocode.     See  Cavum  septi  pel- 

lucidi. 
Psychogenesis,  the  development  of 
mind,    249,    256,    257,    294,    305, 
312-316 
Psychology,  general,  297 

physiological,  297 
Pulvinar,    a    visual    center    in    the 
thalamus,  150,  162,  163,  164,  167, 
170,  208,  212,  284,  306 
Purkinje,  cells  of,  51,  52,  190,  191, 

192 
Purple,  visual,  207 
Putamen,  a  part  of  the  Nucleus  lenti- 

formis. 
Pyramid  (pyramis),  an  eminence  on 
the  ventral  surface  of  the  medulla 
oblongata  produced  by  the  pjTa- 
midal  tract  and  from  which  the 
latter  receives  its  name,  114,  155 
Pjrramids,  decussation  of,  131 
Pyriform  lobe.    See  Lobe,  pyriform. 


346 


INDEX    AND    GLOSSARY 


Quale,  a  quality  pertaining  to  any- 
thing; specifically  a  quality  of  sen- 
sation or  other  conscious  process, 
249,  261,  308,  309,  311 

Rabbit,  cortico-spinal  tract  of,  310 
development  of  eye  of,  204 
spinal  cord  of,  133 
Radiations,  sensory,    the    thalamo- 
cortical    tracts.       See     Tract, 
thalamo-cortical,     and     Corona 
radiata,  287,  289 
auditory,  170,  287 
gustatory,  287 

olfactory,       the      olfacto-cortical 
tracts;  the  term  has  also  been 
applied   to   various   subcortical 
olfactory  tracts,  287 
optic,  170,  210,  287 
somesthetic  (of  tactile  and  general 
sensation),  287 
Radix.     See  Root. 
Rage.     See  Anger. 
Ram6n  y  Cajal,  S.,  42,  44,  48,  50- 
53,  55,  190,  191,  214,  237,  239,  240, 
270-273,  278 
Ramus  communicans,   a  communi- 
cating branch  between  the  ganglia 
of  the  sympathetic  Trunk  and  the 
roots  of  the  spinal  nerves,  125,  126, 
225,  228 
Range  of  behavior,  19,  303 
Ranvier,    node   of.      See   Node   of 

Ranvier. 
Rat,  nervous  system  of,  220 
Rate  of  nervous  conduction,  97,  98 
Reaction,  a  change  in  bodily  state 
in  response  to  stimulation;  cf. 
Reflex,  66 
avoiding.    See  Reflex,  avoiding, 
discriminative,  98,  258,  302,  308 
time,   the   time   required   for   re- 
sponse to  stimulation,  98,  258, 
259 
Reading,  apparatus  of.    See  Speech, 

apparatus  of. 
Receptor,  a  sense  organ,  25,  38,  69 
contact,  a  sense  organ  adapted  to 
respond  to  impressions  from  ob- 
jects in  contact  with  the  body; 
opposed  to  distance  Receptor, 
distance,  a  sense  organ  adapted  to 
respond  to  impressions  from  ob- 
jects remote  from  the  body,  23 


Recess,  epitympanic,  195 

infundibular,  118,  119 

lateral,  the  widest  part  of  the 
fourth  Ventricle  under  the  cere- 
bellum. 

optic,  the  depression  in  the  lateral 
wall  of  the  diencephalon  formed 
by  the  evagination  of  the  optic 
Vesicle,  116-119 

utricular.     See  Utricle. 
Reflex  act,  a  simple  form  of  inva- 
riable   Behavior   requiring    a 
nervous  system,   25,   32,   56, 
109,  363 
time  of.     See  Reaction  time. 

alhed,  57,  58,  59,  61 

antagonistic,  57,  58,  59,  61 

arc.     See  Reflex  circuit. 

avoiding,  251,  253,  258 

of  brain  stem,  181,  192,  279,  280, 
304,  305 

bulbar,  181,  279 

chain,  57,  58,  60,  61,  308 

circuit,  a  chain  of  neurons  which 
function  in  a  Reflex  act,  25,  42, 
56,  58,  60,  62,  63,  66,  109,  113, 
132,  133,  134,  260,  308,  309, 
311 

conditional,  242 

cortical,  286,  290 

cycMc,  61,  309 

discriminative.  See  Reaction,  dis- 
criminative. 

of  feeding;  cf.  Oral  sense,  219,  279 

locomotor,  134 

of  medulla  oblongata,  181,  279 

myenteric,  241 

pattern,  65,  219,  305,  307,  312 

proprioceptive,  130,  175-193 

of  spinal  cord,  129,  131-135,  174, 
176,  179-182,  185,  234,  258,  279, 
304,  305 

thalamic,  163,  166,  174,  181,  253, 
254,  304,  306,  311 
Regeneration  of  nervous  tissues,  46, 

132 
Region,  cortical,  a  group  of  related 

cortical  Areas,  273,  276 
Regulation,  the  process  of  adapta- 
tion of  form  or  behavior  of  an  or- 
ganism to  changed  conditions,  31 
Reil,  island  of.    See  Insula. 
Reinforcement,  59,  62,  63,  101,  192, 

218 


INDEX    AND    GLOSSARY 


347 


Reissner,  membrane  of.    See  Mem- 
brane, vestibular. 
Reptiles,  cerebral  cortex  of,  216 
Resistance,  nervous,  104,  252,  258, 

295,  296,  304,  307 
Resolution,    physiological,    58,    293, 

304,  306,  307 
Respiratory  apparatus,  89,  144,  147, 

232,  234-240 
Restifonxi  body.     See  Corpus  resti- 

forme. 
Reticular  formation.     See  Formatio 

reticularis. 
Retina,  123,  146,  204,  208 

pigment  of,  205,  207,  208,  211 
Retraction  of  the  neuron,  103,  104 
Retzius,  G.,  85,  88,  124,  197,  203, 

219 
Reverberation,  cortical,  293,  296 
Rhinencephalon    (nose    brain),    the 
olfactory  part  of  the  brain.   111, 
112,  118,  119,  123,  215,  273 
Rhodopsin,  207 

Rhombencephalon,  that  part  of  the 
brain  below  the  Isthmus,  includ- 
ing the  Medulla  oblongata  and 
Cerebellum,  116-119,  121,  122, 
123,  143 
development  of,  116-119 
Rivers,  W.  H.  R.,  94,  95,  142 
Rod  of  CoRTi  (piUar  of  Corti),  197, 
198 
of  retina,  205,  206,  207,  208,  211 
Rolando,    fissure    of.      See   Sulcus 
centralis, 
gelatinous     substance     of.       See 
Substantia  gelatinosa  Rolandi. 
Root  (radix),  a  nerve  root,  or  the 
part  of  a  nerve  adjacent  to  the 
center   with    which    it    is    con- 
nected ;  in  the  case  of  spinal  and 
cranial  nerves,    the  part  lying 
between  the  cells  of  origin  or 
termination  and  the  ganglion, 
anterior.    See  Root,  ventral, 
dorsal    (radix    dorsalis,   posterior 
root,  radix  posterior),  the  dorsal 
or  sensory  Root  of  a  spinal  or 
cranial    norvo,    126,    128,    129, 
130,  133,  134,  139,  150,  151, 227, 
228,  252 
posterior.     See  Root,  dorsal, 
spinal,   composition  of,    126.   135, 
136,  150,  151,  225,  227 


Root,  ventral  (radix  ventralis,  radix 
anterior) ,  the  ventral  or  motor  root 
of  a  spinal  or  cranial  nerve,  126, 
128,  129,  130,  133,  134,  150,  151, 
182,  227 

Rostral,  pertaining  to  the  beak  or 
snout,  or  directed  toward  the 
front  end  of  the  body  as  opposed 
to  Caudal. 

Rostrum  of  corpus  callosuin,  119 

Russell,  J.  S.  Riesen,  194 


Sac,  dorsal  (saccus  dorsalis),  a  dorsal 

evagination  of  the  Tela  chori- 

oidea  of   the  third  ventricle  in 

some  vertebrate  brains. 

endolymphatic       (saccus       endo- 

lymphaticus) ,  196 
nasal,  110,  111 
Saccule  (sacculus),  part  of  the  mem- 
branous labyrinth  of  the  ear,  85, 

183,  195,  196,  199,  200,  201 
Sachs,  E.,  171 

Sala,  C.  L.,  so 

SaUva,  secretion  of.    See  also  Gland, 

salivary  146,  147,  241,  242,  247 
Sarcophaga  carnaria,  nervous  system 

of,  30 
Scala  media.    See  Ductus  cochlearis. 

tympani,  197 

vestibuh,  197 
Scarpa,  ganglion  of.    See  Ganglion, 

vestibular. 
Schaefer,  E.  a.,  214 
Schaper,  a.,  194 
scohnemann,  a.,  203 
ScHULTZE,  tract  of  (comma  tract). 

See  Fasciculus  interfascicularis. 
ScHW'ALBE,    vestibular    nucleus    of, 

184,  185 

Schwann,    sheath   of.      See   Neuri- 
lemma. 

Scyllium,  nervous  system  of,  110 

Sea-robin,   nervous  system  of,   151, 
153 

Secretin,  224 

Secretions,  effect  of  fatigue  and  emo- 
tion on,  103,  255 
internal,  163,  224,  231,  255,  256 
psychic,  241,  242 

Segment,  mesodermal,  or  primitive. 
See  Somites. 


348 


INDEX    AND    GLOSSARY 


Segmental    apparatus,     the    Brain 

stem,  113,  114,  123 
Segmentation  of  nervous  system,  28, 

29,  30,  113,  125,  144,  150 
Self-consciousness,  314 
Senility,  316 
Semicircular  canals,  nerve  endings  in, 

88,89 
Semon,  R.,  295 

Sensation,   a  subjective   experience 
arising  in  response  to  stimula- 
tion, 70,  108,  249,  250,  256,  257, 
261 
common,  259 
in  lower  animals,  72 
neurological   mechanism   of,   250, 

257  261 
viscer'al,  77,  91,  148,  228,  234-246, 
250,  259 
Sense,  criteria  of,  74 

organ.     See  Receptor. 
Sentiments.     See  Affection. 
Septum,  the  medial  wall  of  the  cere- 
bral   hemisphere    between    the 
Lamina  terminalis  and  the  ol- 
factory Bulb;  in  man  its  upper 
part  is  thin  and  forms  the  Sep- 
tum pellucidum,  219,  220,  306 
dorsal  median,  of  cord.  See  Fissure, 

dorsal, 
pellucidum,  a  thin  sheet  of  nervous 
tissue  forming  a  portion  of  the 
medial  wall  of  each  cerebral 
hemisphere  between  the  Corpus 
callosum  and  the  Fornix,  162 
Sexual  organs,  innervation  of,  232 

sensations  from,  89 
Shambaugh,  G.  E.,  198,  199,  203 
Shark,    nervous    system    of.      See 

Fishes,  nervous  system  of. 
Sheath,     medullary.       See     Myelin 
sheath, 
myehn.     See  Myelin  sheath, 
primitive.    See  Neurilemma, 
of  Schwann.    See  Neurilemma. 
Sheldon,  R.  S.,  95,  248 
Sherren,  J.,  94,  142 
Sherrington,  C.  S.,  35,  37,  65,  68, 
75,  77,  95,  124,  134,  142,  172,  180, 
194,  243,  250,  259,  260,  262,  281, 
282,  300 
Sight,  organs  of.    See  Visual  appara- 
tus. 
Sinus,  inferior,  of  labyrinth,  196 


Skin  brain,  112,  123 
nerves  of.    See  Nerves,  cutaneous, 
nerve-endings  in,  79,  80,  81-83,  84, 

86,  245,  253 
sensibihty  of,  70,  72,  79,  80-86, 
132,     172-180,     212,     228-230, 
245,  249,  250,  252,  253,  260 
Sleep,  103,  104,  297 
Smell,  organs  of.    See  Olfactory  ap- 
paratus. 
Smith,  G.  Elliot,  263,  273,  278 
Sneeze,  mechanism  of,  238 
Social  evolution,  314,  315 
Somatic  area.    See  Area,  somatic. 
cortex.     See  Neopallivmi. 
nerves.     See  Nerve,  somatic. 
organs,  those  concerned  with  the 
adjustment  of  the  body  to  its 
environment,   76,   79,   92,    109, 
172 
Somesthetic  apparatus,  the  general 
somatic  sensory  systems,  includ- 
ing cutaneous  and  deep  sensibil- 
ity, 164,  165,  172-180 
Somites    (myotoms,    primitive   seg- 
ments,    mesodermal     segments), 
segmented  masses  of  mesoderm  in 
vertebrate    embryos    which    give 
rise  to  the  somatic  muscles,  92 
Sound,  reaction  time  to,  98 

receptors  for.     See  Auditory  ap- 
paratus. 
Space,  discrimination  of,   130,   132, 
137,  172,  178-180 
of  NuEL,  197 

perforated.     See  Substantia  per- 
forata. 
Speech,  apparatus  of  (including  read- 
ing and  writing);  cf.  Aphasia,  283, 
291-293 
Spencer,  Herbert,  17 
Sphere,  cortical.    See  Center,  corti- 
cal. 
Spiders,  nervous  system  of,  29 
Spielmeyer,  W.,  284 
Spinal  cord  (medulla  spinalis),  that 
portion  of  the  central  nervous 
system  contained  within  the 
spinal    Canal    of    the   spinal 
column,    106,    107,    110-112, 
117,  118,  120,  122,  125,  126, 
127,   128-130,  150,   151,    182 
cervical,  128,  129,  130 
development  of,  182 


INDEX    AND    GLOSSARY 


349 


Spinal  cord,  functions  of,  129,  132, 
182,  234,  237,  238,  251-253, 
304,  311 
lesions   of,    173,   175,  178,  179, 

237,  238,  251 
tracts    of,    130,   139,   141,   174, 
176 
Spiracle,  a  rudimentary  gill  cleft  in 
some  fishes,  represented  in  mam- 
mals bv  the  auditory  or  Eusta- 
cheantube,  110,  111,  112 
Spitzka,  E.  C.,  108 
Splanchnic,  visceral,  76 
Spongioblast,  one  of  the  epithelial 
cells  of  the  embryonic  Neural  tube 
which  becomes  transformed  into 
an  Ependyma  cell. 
Spurzheim,  J.  K.,  280,  281,  300 
Stabler,  Eleanor  M.,  75 
Stalk,  optic,  204 
Steiner,  J.,  135,  142 
Stem.     See  Brain  stem. 
Stiles,  P.  G.,  101,  105,  248 
Stilling,    dorsal   nucleus    of.      See 

Nucleus,  dorsal,  of  Cl.ark. 
Stimulus,  a  force  which  excites  an 
organ  to  activity,  69 
adequate,  25,  38,  70,  76 
Stomach,  144, 147, 224,  234, 239, 240- 

243 
Streeter,  G.  L.,  200,  203 
Stria    acustica.     See    Stria    medul- 
laris  acustica. 
of  Baillakger.    See  Line  of  Bail- 
larger. 
of  Gennari.     See  Line  of  Gen- 

nari. 
longitudinalis    (stria    of    Lancisi, 
nerve  of  Lancisi),  slender  bun- 
dles    of     nerve-fibers    running 
along  the  dorsal  surface  of  the 
Corpus  callosum  in  the  floor  of 
the  longitudinal  fissure. 
medullaris     acustica,     secondary 
acoustic  fibers  arising  in  the 
dorsal   cochlear  nucleus   and 
decussating   across   the   floor 
of    the    fourth    ventricle    to 
reach     the    opposite    lateral 
Lemniscus,  201 
thalami,  a  band  of  fibers  accom- 
panying  the   Taenia   thalami 
along  the  dorsal  border  of  the 
thalamus,  containing  the  trac- 


tus     olfacto-habenularis,     tractus 
cortico-habenularis,      and      other 
fibers,  162,  165,  166,  167,  220 
Stria,   olfactoria  intermedia,  a  sec- 
ondary olfactory  Tract  from 
the  olfactory  Bulb  to  the  Tu- 
berculum   olfactoriimi,   most 
of    its    fibers    first    crossing 
in  the  anterior  Commissure, 
219 
lateralis,  a  secondary  olfactory 
Tract  from  the  olfactory  Bulb 
to    the    Nucleus    olfactorius 
lateralis,  219 
medialis,  a  secondarj^  olfactory 
Tract  from  the  olfactory  Bulb 
to    the    Nucleus    olfactorius 
medialis,  219 
semicircularis.    See  Stria  tennina- 

Us. 
terminalis  (stria  semicircularis,  old 
term,    tsenia    semicircularis),    a 
correlation    tract    between    the 
Nucleus  amygdalae  of  the  lateral 
olfactory  Area  and  the  medial 
olfactory  Area,  114,  162,  267 
vascularis  of  cochlea,  197 
Striate  area.    See  Area  striata, 
body.     See  Corpus  striatum. 
Stripe  of  Baillarger.    See  Line  of 
Baillarger. 
of  Gennari.    See  Line  of  Gennari. 
of  Hensen,  197,  198 
Stirrgeon,   nervous  system  of,    151, 

152 
Subconscious    mind.      See    Uncon- 
scious cerebration. 
Subiculvmi,  that  part  of  the  Gjtus 
hippocampi    which    borders     the 
fissura  hippocampi;  sometimes  ap- 
phed  to  the  whole  of  this  g^TUs, 
222 
Substance,   black.     See   Substantia 
nigra, 
chromophilic  (Nissl  substance,  ti- 
groid  substance,   or  bodies,   or 
granules),   a   proteid   substance 
topically  present  in  the  cyto- 
plasm of  nerve-cells,  40,  41,  42, 
45,  46,  48,  99,  102,  1.36.  2S4 
gray.     See  Matter,  gray, 
perforated.     See  Substantia  per- 
forata, 
white.    See  Matter,  white. 


350 


INDEX    AND    GLOSSARY 


Substantia  alba.    See  Matter,  white, 
gelatinosa  Rolandi  (gelatinous  sub- 
stance of  Rolando),  an  area  of 
Neuropil   bordering   the   dorsal 
gray  column  of  the  spinal  cord; 
sometimes  also  applied  to  the 
nucleus  of  the  spinal  V  tract  in 
the  medulla  oblongata,  129 
grisea.    See  Matter,  gray, 
nigra  (black  substance),  an  area  of 
gray  matter  immediately  dor- 
sal   of    the    Basis    pedunculi, 
functionally     related     to     the 
cortico-pontHe  tracts,  161,  165, 
167,  210 
perforata,  anterior  (anterior   per- 
forated substance  or  space), 
a  region  on  the  ventral  sur- 
face of  the  brain  in  front  of 
the  optic   Chiasma  which  is 
pierced  by  many  small  arte- 
ries, 120,  219,  306 
posterior    (posterior   perforated 
substance  or  space),  a  region 
on  the  ventral  surface  of  the 
brain  between  the  Bases  pe- 
dunculi which  is  pierced  by 
small  arteries,  120 
Subthalamus,    the   ventral   part   of 
the  Thalamus,  163,  165,  166,  167, 
174,  176,  306 
Sulcus,    in    the    cerebral    cortex,    a 
superficial    fold    not    involving 
the  entire  thickness  of  the  brain 
wall;  cf.  Fissure,  266 
anterior  parolfactory,  119 
central  (fissure  of  Rolando,  cru- 
ciate sulcus),  119,  121,  281,  282 
cinguh,  119 
corporis  callosi,  119 
cruciate.    See  Sulcus,  central, 
frontahs,  inferior,  121 

superior,  121 
interparietahs,  121 
limiting  (sulcus  limitans),  a  longi- 
tudinal groove  on  the  ventricu- 
lar   surface   of    the    embryonic 
brain     separating     the     dorso- 
lateral sensory  Plate  from  the 
ventro-lateral  motor  Plate,  36, 
117,  118,  120,  153,  181 
.    occipitalis  trans  versus,  121 
posterior  parolfactory,  119,  219 
precentralis,  121 


Sulcus  rhinaUs.    See  Fovea  limbica. 

spiralis,  197,  198,  199 
Summation,   central.     See  Conduc- 
tion, avalanche,  and  Reinforce- 
ment, 
of    stimuli,    the   enhancement   of 
effect  by  repeated  stimulation, 
59,  62,  63,  192,  208,  218,  258, 
260,  268,  307 
Suprasegmental  apparatus,  the  cere- 
bral cortex  and   cerebellum   with 
their     immediate      dependencies, 
^  113,  120,  123,  143,  158,  186 
Susceptibility  of  neurones  to  poisons, 
^  97,  231 

Swallowing,  apparatus  of,  78,  247 
Sylvius,  aqueduct  of.    See  Aqueduct 
of  Sylvius. 
fissure  of.    See  Fissure,  lateral. 
fossa  of.    See  Fossa  lateralis. 
Symbolizing,  defects  of,  292 
Sympathetic  nervous  system.     See 

Nervous  system,  sympathetic. 
Synapse,  the  place  where  the  nervous 
impulse  is  transmitted  from  one 
nem-on  to  another,  50,  51,  52, 
53,  54,   96,  97,   103,   109,   190, 
218,  231,  252,  268,  269,  272,  295 
fatigue  of,  102,  103 
time  of  transmission  through,  54, 
98,  99 
Synergic    muscles.      See    Muscles, 

synergic. 
System,  functional,  all  neurons  of 
common  physiological  type.  Most 
peripheral  nerves  contain  several 
components  belonging  to  different 
systems,  145-150 


TabaUus  bovinus,  nervous  system  of, 
30 

Taenia,  the  Une  of  attachment  of  a 
membranous  part  to  a  massive 
part  of  the  brain  wall;  formerly 
appUed  also  to  some  fiber 
tracts,  as  Taenia  semicircularis 
=  Stria  terminalis,  and  Taenia 
thalami  =  Stria  meduUaris 
thalami. 
chorioidea,  the  hne  of  attachment 
of  the  lateral  chorioid  Plexus  to 
the  medial  wall  of  the  cerebral 


INDEX    AND    GLOSSARY 


351 


hemisphere.     (This  porliou  of  the 
medial  wall  is  adherent  to  the  thal- 
amus, forming  the  Lamina  affixa.) 
Taenia  fornicis,  the  line  of  attach- 
ment   of    the    lateral    chorioid 
Plexus   to  the   Fimbria  of  the 
Fornix.  j 

thalami,  the  line  of  attachment  of  j 
the  Tela  chorioidea  of  the  third  i 
ventricle  to   the  dorsal  margin  | 
of  the  thalamus.    This  name  was 
formerly  apphcd  to  a  band  of 
fibers,     the     Stria     medullaris 
thalami,     which     borders     the 
tienia.  162. 
ventriculi  quarti,  the  line  of  at- 
tachment  of   the   membranous 
roof  of  the  fomth  ventricle  to 
the  medulla  oblongata,  155. 
Tashiro,  S.,  97,  105 
Taste,  apparatus  of.    See  Gustatory 
apparatus, 
bud,  91,  143,  144,  21S,  243,  245, 

246 
peripheral  nerves  of.    See  Nerves, 
gustatorj'. 
Taxis.     See  Tropism. 
Tectum  mesencephali,   the  roof  of 
the    midl^rain,    comprising    the 
Colliculus  superior  (tectum  op- 
ticum)  and  the  Colliculus  infe- 
rior, 161,  246 
optic.    See  Colliculus,  superior. 
Teeth,  85,  146,  249 
Tegmen  ventriculi  quarti,  the  roof  of 
the  fourth  ventricle,  formed  chiefly 
bv  the  Velum  meduUare  anterius, 
the   Velum   meduUare    posterius, 
and  the  Plexus  chorioideus  ven- 
triculi quarti. 
Tegmentum,  the  dorsal  part  of  the 
cerebral    Peduncle    between    the 
Basis  pedunculi  and  the  Aqueduct 
of  Sylvius ;  often  described  as  also 
extending  baclvward  into  the  cor- 
responding  part   of   the   medulla 
oblongata,  15S,  181,  182 
Tela,  any  thin  non-nervous  part  of 
the  brain  wall. 
chorioidea,    that    portion    of    the 
Pia    mater    which    covers    any 
tliin    non-nervous   part    of    the 
brain  wall,  including  the  chori- 
oid Plexuses. 


Telencephalon  (cndbrain),  the  ante- 
rior    end     of     the     embryonic 
Neural  tube  and  its  adult  de- 
rivatives, comprismg  chiefly  the 
cerebral  hemispheres  and  Lam- 
ina   terminalis,    117-119,    121- 
123,  160 
mediiun,  that  portion  of  the  em- 
bryonic Telencephalon  which  is 
not  evaginated  to  form  the  cere- 
bral hemispheres;  it  comprises 
chiefly   the   Lamina   terminaUs 
and   Pars   optica   hypothalami, 
122 
Telodendron,  the  termmal  branched 
end  of  a  Dendrite;  sometmies  ap- 
plied also  to  that  of  an  Axon;  cf. 
Terminal  arborization. 
Temperatm-e,  apparatus  of,  71,  84, 
131,  132,  137,  138,  139,  141,  163- 
167,  172-174,  242,  254,  260 
Tendon,  nerve  endings  in,  87 

sense,  77,  87,  132 
Tentorium    cerebelli,    a    transverse 
fold  of  Dura  mater  between  the 
cerebellum  and  the  cerebral  hemi- 
spheres. 
Terminal  arborization,  the-  branched 
end  of  an  axon;    sometimes  ap- 
phed  also  to  that  of  a  Dendrite, 
40 
Termmology.    See  Nervous  system, 

terminology  of. 
Testes.    See  Colliculus,  inferior. 
Thalamencephalon.    See  Dienceph- 

alon. 
Thalamus,    the   middle    and    larger 
subdivision    of    the    Dienceph- 
alon,  sometimes  applied  to  the 
entire  diencephalon  and   called 
Thalamus  opticus,  63,  112,  114, 
117,    121-123,    141,    162,    163, 
164-166,    167,    174,    176,    204, 
210,  279,  311 
lesions  of,  253,  254,  279 
new.     See  Neothalamus, 
old.     See  Palaeothalamus. 
opticus;     See  Thalamus, 
pain  center  in,  167,  253,  254,  258, 

260,  261,  311 
respiratory  center  in,  240 
Thirst,  apparatus  of,  89 
Thompson,  T.,  142,  175,  179,  262 
Thorns  of  dendrites,  272 


352 


INDEX    AND    GLOSSARY 


Threshold,    the    minimal    stimulus 
which  will  excite  an  organ  to  ac- 
tivity, 72,  80,  91,  132,  172,  218, 
252,  254,  255 
Tickle,  76,  254 

Tigroid  bodies,  substance,  or  gran- 
ules.     See    Substance,    chromo- 
philic. 
Time,  central.     See  Pause,  central, 
latent.     See  Pause,  central, 
reaction.     See  Reaction  time. 
Tissue,  the  cellular  fabric  of  which 

the  body  is  composed,  24 
TiTCHENER,  E.  B.,  70 
Tone,  affective.      See  Feehng  tone 
and  Affection, 
analysis,  198,  199,  202 
feeling.       See   Feehng   tone  and 

Affection, 
muscular,  77,  89,  189,  192 
nervous,  101,  192 
Tongue,  muscles  of,  92,  144,  147,  148 
nerves  of,  143,  144,  146-148,  243, 
245 
Touch,  apparatus  of,  62,  70,  79,  SO- 
BS, 131,  132,  137,  138,  139,  141, 
163-167,  172-180,  242,  243,  245, 
252,  253,  257,  260 
reaction  time  of,  98 
Toxines.     See  Poisons. 
TozER.  F.  M.,  180 
Tract  (tractus),  a  collection  of  nerve- 
fibers  of  like  origin,  termination, 
and  function;  cf.  Fasciculus,  27, 
100,  128,  304 
association;  cf.  Fibers,  association, 

58,  64,  267,  285 
bulbo-spinal,  157 
central  tegmental,  188 
cerebello-tegmental,  188 
comma.     See  Fasciculus  interfas- 

cortico-bulbar,  161,  169,  170,  181 

cortico-cerebellar.  See  Tract,  cor- 
tico-pontile. 

cortico-mesencephalic,  289 

cortico-oculomotor,  170 
.  cortico-pontUe,  161,  169,  170,  187, 
188,  289 

cortico-rubral,  170,  289 

cortico-spinal  (fasciculus  cerebro- 
spinahs,  B.  N.  A.,  pyramidal 
tract),  the  voluntary  motor 
path  from  the  precentral  gy- 


rus of  the  cerebral  cortex  to  the 

spinal  cord,  where  it  divides  into 

lateral  and  ventral  parts,  128,  130, 

131,  140,  141,  156,  161,  167,  168, 

170,  181,  188,  192,  282-285,  289, 

293,  310,  311 
Tract,  cortico-spinal,  lateral  (fas- 
ciculus cerebro-spinalis  later- 
ahs,  B.  N.  A.,  lateral  or 
crossed  pyramidal  tract),  130, 
131,  141 
ventral  (fasciculus  cerebro- 
spinahs  anterior,  B.  N.  A., 
ventral  or  direct  pjramidal 
tract,  column  of  T&rck), 
130,  131,  141 

cortico-thalamic,  289 

direct  cerebellar.  See  Tract, 
spino-cerebellar,  dorsal. 

of  Flechsig.  See  Tract,  spino- 
cerebellar, dorsal. 

of  GowERS.  See  Fasciculus  ven- 
tro-laterahs  superficialis. 

habenulo-peduncular  (fasciculus 
retrofiexus,  Meynert's  bundle), 
165,  220 

of  Helwig.  See  Tract,  olivo- 
spinal. 

intemuncial,  a  fiber  tract  connect- 
ing two  nuclei  or  centers,  65 

of  LissAUER.  See  Fasciculus  dor- 
so-laterahs. 

of  LowENTHAL.  See  Tract,  tecto- 
spinal. 

mamiUo-peduncular,  161,  220 

mamillo-thalamic  (fasciculus 

thalamo-mamillaris   B.    N.    A., 
tract  of  ViCQ  d'Azyr),  165,  220 

mesencephalic,  of  V  nerve,  161 

of  Meynert.  See  Tract,  haben- 
ulo-peduncular. 

of  MoNAKOW.  See  Tract,  rubro- 
spinal. 

nomenclature  of,  128 

olfactory  (tractus  oHactorius),  ol- 
factory fibers  of  the  second 
order  passing  from  the  olfac- 
tory Bulb  to  the  nuclei  of  the 
Area  olfactoria.  See  Stria  ol- 
factoria,  114,  120,  165,  217,  218, 
219,  220 

ohacto-hypothalamic,  220 

olfacto-tegmental,  220,  221 

ohvo-cerebellar,  155,  176,  188 


INDEX    AND    GLOSSARY 


353 


Tract,  olivo-spiiial  (HiihWHi's  bun- 
dle,   tractus  triangularis),   130, 
131 
optic   (tractus  opticus),   that  por- 
tion  of   the   optic   i)ath   which 
passes  between   the  optic  Chi- 
asma  and  the  optic  centers  in 
the     thalamus     and    midi^rain. 
(The   term   might   properly   be 
extended  to  include  also  the  so- 
called   optic   Nerve),   114,   120, 
161,   166,    1G7,    208,    209,    210, 
222 
ponto-cerebellar,  188 
predorsal.    See  Tract,  tecto-spinal. 
projection.    See  Projection  fibers, 
pj-ramidal.      See    Tract,    cortico- 
spinal. 
respiratory,  240 
rubro-spinal  (Monakow's  tract), 

130,  131,  156,  161,  188,  189 
rubro-thalamic,  188 
of  ScHULTZE.     See  Fasciculus  in- 
ter fascicularis. 
secondary  gustatory.     See  Lem- 
niscus, visceral, 
visceral.     See   Lemniscus,  vis- 
ceral. 
septo-marginal,  130,  131 
solitary.    See  Fasciculus  solitarius. 
solitai'io-spinaUs,    237,    239,    240, 

247 
of  spinal  cord.     See  Spinal  cord, 

tracts  of. 
spinal,  of  V  nerve,  148,  149,  153, 
155,  156,  174,  180,  244 
of  vestibular  nerve,  155 
spino-cerebellar,  114,  137,  ISO 
dorsal   (fasciculus  cerebello-spi- 
nalis,  B.  N.  A.,  direct  cere- 
bellar tract,  Flechsig's  tract), 
130,  139,  156,  176,  188 
ventral   (part  of  Goa^'ers'   fas- 
ciculus, or  Fasciculus  antero- 
laterahs   superficialis,    B.    N. 
A.),  128,  130,  139,  156,  176, 
188 
spino-olivary,  130,  131,  176,  188 
spino-tectal,    128,    130,    131,    161, 

179 
spino-thalamic,  lateral,   130,   131, 
139,  179 
ventral,  130,  131,  139 
tecto-cerebellar,  176,  188 

23 


Tract,  tecto-spinal  (predorsal  bundle, 
tract  of  Lowenthal),  130,  131, 
140,  156 

terminology  of,  128 

thalamo-bulbar,   181 

thalamo-cortical;  cf.  Projection 
fibers  and  Radiations,  170,  174, 
176,  289,  306 

thalamo-olivary,  161 

thalamo-peduncular,  165 

thalamo-spinal,  181 

triangular.  See  Tract,  oUvo-spinal. 

vestibulo-cerebellar,  157,  176,  187, 
188 

vestibulo-spinal,  130,  131,  140, 
157,  176,  185 

of     ViCQ     d'Azyr.       See     Tract, 
mamillo-thalamic. 
Transmission    of    nervous    impulse. 

See  Conduction,  nervous. 
Trapezoid  body.     See  Body,  trape- 
zoid. 
Trigonum   habenulae,    a   triangular 
area  at  the  posterior  end  of  the 
Habenula,  162 

hypoglossi  (eminentia  hypoglossi), 
a  ridge  in  the  floor  of  the  fom-th 
ventricle  produced  by  the  XII 
nucleus,  154,  156 

olfactorium,  a  triangular  expan- 
sion of  the  Crus  olfactoria  from 
which  the  Striae  olfactorias  arise. 

vagi.    See  Ala  cinerea. 
Tropism,  a  simple  form  of  invariable 

Behavior  not  requiring  a  nervous 

system,  57 
Trotter,  W.,  79,  84,  95,  172 
Trunk  (truncus),  the  main  stem  of  a 
nerve  from  which  the  branches 
(rami)  are  given  off.    See  Nerve. 

sympathetic  (ganglionated  symjia- 
thetic  cord,  sympathetic  chain, 
vertebral  sympathetic  chain),  a 
strand  of  sympathetic  nerves 
and  ganglia  extending  along 
each  side  of  the  vertebral  col- 
umn, 107,  225,  226 
Tube,  auditory  (Eustachcan  tube), 
195 

nem-al.     See  Neural  tube. 
Tuber  cinereum,   a  gray   eminence 

forming  the  ventral  part   of   the 

Hypothalamus,     114,     119,     120, 

163,  167,  306 


354 


INDEX    AND    GLOSSARY 


Tubercle,  anterior,  of  thalamus,  an 

eminence   on   the   dorsal   surface 
formed  by  the  Nucleus  anterior 
thalami,  162 
Tuberculum    acusticum    of     fishes 
(part  of  the  Area  acustico- 
lateralis),  148,  149,  152,  200 
of  mammals  (the  dorsal  cochlear 
nucleus),  201 
cinereum,    an    eminence    on    the 
lateral   aspect   of   the   medulla 
oblongata  produced  chiefly  by 
the  spinal  V  tract  and  its  nu- 
cleus. 
cuneatum,    an    eminence   on    the 
dorsal  surface  of  the  lower  end 
of  the  medulla  oblongata  later- 
ally of  the  Clava  produced  by 
the  nucleus  of  the  Fasciculus 
cuneatus,    130,    139,    141,    156, 
164,  176,  177,  188 
fasciae  dentatse,  220 
oUactorium    (lobus   parolfactorius 
of  Edinger),  the   intermediate 
olfactory  Nucleus,  lying  in  the 
Substantia  perforata  anterior ;  cf . 
Area  olfactoria,  219,  220,  273 
Tunnel  of  Corti,  197 
TuKCK,  column  of,  the  ventral  cor- 

tico-spinal  Tract. 
Turner,  W.  A.,  194 
Tympanic  membrane.   Tympanum. 
See  Membrane,  tympanic. 

Unconscious   cerebration,  297,  309, 
311 

mind,  296,  297,  309 
Unconsciousness,  297 
Uncus,  the  hook-shaped  extremity  of 

the  Gyrus  hippocampi,  part  of  the 

Archipallium,  219,  273 
Unpleasantness.     See  Affection. 
Utricle  (utriculus,  recessus  utricuh), 

part  of  the  membranous  labjTinth 

of  the  inner  ear,  85,  183,  195,  196, 

200,  201 

« 
Valve  of  ViEussENS.      See  Velum 

meduUare  anterius. 
Valvula  cerebelli .    See  Velum  me  dul- 

lare  anterius. 
Variable   behavior.      See   Behavior, 

variable. 


Variation,  negative,  in  nerve-fibers, 

96 
Varoli     (Varolius).       See     Pons 

Varolii. 
Vas  spirale,  197 

Vasomotor    apparatus,    the    neuro- 
muscular mechanism  which  con- 
trols the   amount  of  blood   sup- 
pUed  to  any  part,  104,  114,  232, 
234,  235 
Veins,  nerves  of.    See  Vasomotor  ap- 
paratus. 
Velocity     of     nervous     conduction. 
See  Nervous  impulse,  velocity  of. 
Velum  anticum.    See  Velum  medul- 
"lare  anterius. 
interpositum,  the  Tela  chorioidea 

of  the  third  ventricle. 
medullare  anterius,  a  thin  portion 
of  the  brain  wall  containing  a 
few  myeUnated  fibers  which 
forms  the  roof  of  the  fourth 
ventricle  in  front  of  the  cere- 
bellum, 119,  154 
posterius,  a  thin  portion  of  the 
brain  wall  containing  a  few 
myelinated  fibers  which  forms 
a  small  part  of  the  roof  of  the 
fourth  ventricle  immediately 
behind  the  cerebellum, 
superius.    See  Velimi  medullare 
anterius. 
transversum,  a  transverse  fold  of 
the  Tela  chorioidea  which  marks 
the  boundary  between  the  Di- 
encephalon  and  the  Telenceph- 
alon in  the  embryonic  brain. 
Ventral,  on  the  front  or  beUy  side  of 
the  body,  termed  Anterior  in  the 
B.  N.  A.  fists,  115 
Ventricle,  a  cavity  within  the  brain 
and   spinal  cord   derived   from 
the    lumen    of    the    embryonic 
Neural  tube, 
fifth.     See  Cavum  septi  pellucidi. 
first.    See  Ventricle,  lateral, 
fourth  (metaccele),  the  ventricle  of 
the  medulla  oblongata,  119, 121, 
152,  264 
lateral    (paracoele),   the    ventricle 
of    each    cerebral    hemisphere; 
these  are  also  called  first  and 
second  ventricles,  121,  170,  210, 
222, 264 


INDEX    AND    GLOSSARY 


355 


Ventricle,  second.      See   Ventricle, 
lateral, 
third   (diaca'le),   the    ventricle  of 
the  diencephalon,  121,  162,  170, 
264,  265 

Veratti,  E.,  50 

Vermis  cerebelli  (worm),  the  middle 
lobe  of  the  cercbcllmn,  119,  187, 
191,  201  . 

Vertebrates,  behavior  of,  33 
nervous  system  of,  29 

Verworn,  M.,  37,  101 

Vesicle,  optic,  an  outgrowth  from 
the  lateral  wall  of  the  dienceph- 
alon which  forms  the  nervous  part 
of  the  eyeball.  It  first  assumes 
the  form  of  a  simple  hollow  sphere, 
the  primary  optic  vesicle,  which 
later  collapses  to  form  a  two-lay- 
ered optic  cup,  or  secondary  optic 
vesicle,  116,  117,  204 

Vestibular  apparatus,  88,  89,  110, 
111,  131,  145,  147,  150,  183-193, 
199,  200,  201 

Vestiges,  memory,  in  cortex,  295- 
297,  304,  306-308 

Vibrations,  table  of,  72 

Vibrissa?,  innervation  of,  80 

Vicarious  function  in  cortex,  294 

ViCQ  d'Azyr,  tract  of.  See  Tract, 
mamillo-thalamic . 

Vincent,  Stella  B.,  80,  95,  214 

Viscera,  the  internal  organs,  espe- 
cially those  concerned  with  the 
internal  adjustments  of  the  body, 
76,  89,  93,  109,  144,  234-243,  250 

Visceral  apparatus,  224-247,  250,  259 
nerves.     See  Nerve,  visceral, 
brain,  112,  123 

Vision,  stereoscopic,  209,  210 


Visual  apparatus,  62,  63,  71,  86,  110- 
112,  123,  145,  146,  150,  160,  163- 
167,  170,  186,  204-213,  268,  279 

VoGT,  O.,  273,  278,  287 

Voluntary  movement,  apparatus  of, 

78,  166,  181,   192,  222,  240,  241, 

279,  285,  286 
Vomiting,  mechanism  of,  239,  243 

Waldeyer,  W.,  49,  55 

Warmth,  sensations  of.  See  Tem- 
perature, apparatus  of. 

Washburn,  A.  L.,  248 

Washburn,  Margaret  F.,  37 

Watson,  J.  B.,  37,  95,  203,  214,  262 

Weigert,  method  of,  129,  274 

WiLLEMS,  E.,   180 

Willis,  circle  of.  See  Circle  of 
Willis. 

Wilson,  J.  G.,  85,  95,  194,  243,  248 

WooDwoRTH,  R.  S.,  98,  105,  213 

Word-blindness  (Alexia),  292 

Word-deafness,  292 

Worm.     See  Vermis  cerebelli. 

Worms,  nervous  system  of,  27,  28, 
227 

Wrisberg,  nerve  of.  See  Nerve,  in- 
termediate. 

Writing,  apparatus  of.  See  Speech, 
apparatus  of. 

WUNDT,  W.,  98 

Yerkes,  R.  M.,  33,  37,  63,  68 

Zone,  cortical.    See  Center,  cortical. 

of     LissAUER.       See     Fasciculus 

dorso-lateralis. 
of  neural  tube.     See  Plate. 

ZWAARDEMAKER,  H.,  223 


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tive text-book.  It  is  the  only  recent  single  volume  describing  the 
chick  and  pig  embryos  usually  studied  in  the  laboratory,  giving  you  as 
well  a  concise,  systematic  account  of  human  embryology.  The  descrip- 
tions of  the  chick  and  pig  embryos  to  be  studied  in  the  laboratory  cover 
over  100  pages  and  are  illustrated  with  ij2  instructive  illustrations, 
most  of  them  original.  A  large  number  of  original  dissections  of  pig 
and  human  embryos  are  described  and  illustrated,  giving  clear  definite 
directions  for  making  dissections  of  the  nervous  system,  viscera,  face, 
palate,  tongue,  teeth,  and  salivary  glands  of  these  embryos.  Of  the 
same  embryos  from  which  series  of  transverse  sections  have  been  made, 
figures  are  given  showing  the  external  form  and  internal  structure. 
You  can  thus  determine  the  position  and  plane  of  section  of  each  sec- 
tion studied.  Throughout  the  work  a  great  deal  of  information  valu- 
able in  comparative  embryology  and  anatomy  is  given,  so  that  this 
book  will  be  useful  to  every  one  interested  in  vertebrate  embrj-ologj' 
and  anatomy.  In  the  400  large  octavo  pages  you  get  the  very  newest 
advances  in  laboratory  and  classroom  study  of  embryology,  illustrated 
with  368  practical  illustrations,  nearly  40  of  tliem  in  colors. 

Dr.  J.  W.  Papez,  Atlanta  Medical  College:  "  It  is  the  only  book  that 
has  fulfilled  my  needs  exactly.  I  am  using  the  book  this  session  and 
will  continue  to  use  it  in  the  future." 


Saunders'  College  Text-Books 


cFairlaiffidl^i  Bi©l©^ 


Biology:  General  and  Medical.  By  Joseph  McFarland,  M.  D., 
Professor  of  Pathology  and  Bacteriology,  Medico-Chirurgical  Col- 
lege.    i2mo  of  457  pages,  illustrated.     Cloth,  $1.75  net. 

New  (2d)  Edition. 

This  work  is  particularly  adaptable  to  the  requirements  of  scientific 
courses.  There  are  chapters  on  the  origin  of  life  and  its  manifesta- 
tions, the  cell  and  cell  division,  reproduction,  ontogenesis,  conformity 
to  type,  divergence,  structural  and  blood  relationship,  parasitism,  mu- 
tilation and  regeneration,  grafting,  senescence,  etc. 
Prof.  W.  R.  McConnell,  Pennsylvania  State  College:  "It  has  some 
admirable  features,  the  most  valuable  of  which  is  the  careful  resume  of 
the  subjects  of  heredity  and  evolution." 

Dirdw^s    IwwmTtAirBkm    Z©©l©gy 

Invertebrate  Zoology.  By  Oilman  A.  Drew,  Ph.  D.,  Assistant  Di- 
rector of  the  Marine  Biological  Laboratory,  Woods  Hole,  Mass. 
i2mo  of  213  pages.     Cloth,  $1.25  net.  New  isd)  Edition. 

Professor  Drew's  work  gives  the  student  a  working  knowledge  of  com- 
parative anatomy  and  leads  him  to  an  appreciation  of  the  adaptation 
of  the  animals  to  their  environments.  It  is  a  practical  work,  express- 
ing the  practical  knowledge  gained  through  experience.  The  type 
method  of  study  has  been  followed. 

Prof.  John  M.  Tyler,  Amherst  College:  "It  covers  the  ground  well^ 
is  elear  and  very  compact.     The  table  of  definitions  is  excellent." 

Da'Mgk(Birfty^§  E€©iffi©mi€  Z©©l©gy 

Economic  Zoology.  ByL.  S.  Daugherty,  M.  S.,  Ph.  D.,  Professor 
of  Science,  Missouri  Wesleyan  College;  and  M.  C.  Daugherty. 
Part  I — Fieli  and,  Laboratory  Guide:  i2mo  of  237  pages,  inter- 
leaved. Cloth,  $1.25  net.  Part  II — Principles:  i2mo  of  406 
pages,  illustrated.     Cloth,  $2.00  net. 

Not  only  does  this  work  give  the  salient  facts  of  structural  zoology  and 
the  development  of  the  various  branches,  but  also  the  natural  history 
— the  life  and  habits.     It  emphasizes  the  economic  phase  throughout. 

Prof.  V.  E.  Shelf ord,  University  of  Chicago:  "It  has  many  merits 
and  is  the  best  book  of  the  kind  on  the  market." 


Saunders'  College  Text-Books 


Nutritional  Physiology-  By  Percy  G.  Stiles,  Instructor  in  Phys- 
iology at  Harvard  University.  i2mo  of  271  pages,  illustrated. 
Cloth,  $1.25  net. 
Dr.  StUes'  new  work  takes  up  each  organ,  each  secretion  concerned  in 
the  process  of  digestion,  discussing  the  part  each  plays  in  the  physiol- 
ogy of  nutrition— in  the  transformation  of  energy.  In  fact,  the  key- 
note of  the  book  throughout  is  "  energy"-its  source  and  its  conserva- 
tion. The  illustrations  and  homely  similes  are  noteworthy. 
Prof.  M.  E.  Jaffa,  University  of  California:  "The  presentation  of  the 
matter  is  excellent  and  can  be  understood  by  all." 

(BB^  M(iir¥©M§  Sysitdirini 

The  Nervous  System  and  Its  Conservation.  By  Percy  Goldthwait 
Stiles,  Instructor  in  Physiology  at  Harvard  University.  i2mo 
of  230  pages,  illustrated.     Cloth,  $1.25  net. 

Prof.  Stiles'  wonderful  faculty  of  putting  scientific  things  in  language 
within  the  grasp  of  the  non-medical  reader  is  nowhere  better  illustrated 
than  in  this,  his  newest  book.  He  has  a  way  of  conveying  facts  accu- 
rately with  rifle-ball  precision.  This  new  book  is  really  a  physiology 
and  anatomy  of  the  nervous  system,  emphasizing  the  means  of  con- 
serving nervous  energy. 

Introduction  to  Neurology.  By  C  Judson  Herrick,  Ph.  D.,  Pro- 
fessor of  Neurology  in  the  University  of  Chicago.  i2mo  of  360 
pages,  with  137  illustrations.  -^"s'  Out. 

This  work  will  help  the  student  to  organize  his  knowledge  and  to 
appreciate  the  significance  of  the  nervous  system  as  a  working  mechan- 
ism. It  presents  the  actual  inner  workings  of  the  nervous  mechanisms 
in  terms  that  he  can  understand  at  the  very  beginning  of  his  course  in 
psychology,  general  zoology,  comparative  anatomy,  and  general  medi- 
cine. Prof.  Herrick's  many  years  of  teaching  experience  has  impressed 
upon  him  the  difficulties  the  student  finds  in  grasping  this  subject  at 
the  beginning  of  his  course.  He  has  aimed  to  remove  these  difficulties. 
The  text  is  well  illustrated. 


Saunders'  College  Text-Books 


Hadlay  ©im  tKm  IHI©ir§(i 

The  Horse  in  Health  ani  Disease.  By  Frederick  B.  Hadley, 
D.  V.  M.,  Associate  Professor  of  Veterinary  Science,  University 
of  Wisconsin.     i2mo  of  260  pages,  illustrated.     Cloth,  $1.50  net. 

Just  Out. 

This  new  work  correlates  the  structure  and  function  of  each  organ  of 
the  body,  and  shows  how  the  hidden  parts  are  related  to  the  form, 
movements,  and  utility  of  the  animal.  Then,  in  another  part,  you  get 
a  concise  discussion  of  the  causes,  methods  of  prevention,  and  effects 
of  disease.  The  book  is  designed  especially  as  an  introductory  text  to 
the  study  of  veterinary  science  in  agricultural  schools  and  colleges. 


Ka^pp^s  P©MliLiry  CMlftMirci 

Poultry  Culture,  Sanitation,  and  Hygiene.  By  B.  F.  Kaupp,  M.  S., 
D.  V.  M.,  Poultry  Investigator  and  Pathologist,  North  Carolina 
Experiment  Station.     i2mo  of  250  pages,  with  200  illustrations. 

Just  Out. 

This  work  gives  you  the  breeds  and  varieties  of  poultry,  hygiene  and 
sanitation,  ventilation,  poultry-house  construction,  equipment,  ridding 
stock  of  vermin,  internal  parasites,  and  other  diseases.  You  get  the 
gross  anatomy  and  functions  of  the  digestive  organs,  food-stuffs,  com- 
pounding rations,  fattening,  dressing,  packing,  selling,  care  of  eggs, 
handling  feathers,  value  of  droppings  as  fertilizer,  caponizing,  etc.,  etc. 

Lyimck^s  Kidas^s  ©IF  Swiiad 

Diseases  of  Swine.  With  Particular  Reference  to  Hog-Cholera. 
By  Charles  F.  Lynch,  M.  D.,  D.  V.  S.,  Terre  Haute  Veterinary 
College.  With  a  chapter  on  Castration  and  Spaying,  by  George 
R.  White,  M.  D.,  D.  V.  S.,  Tennessee.  Octavo  of  741  pages, 
illustrated.     Cloth,  $S-oo  net. 

You  get  first  some  80  pages  on  the  various  breeds  of  hogs,  with  valu- 
able points  in  judging  swine.  Then  comes  an  extremely  important 
monograph  of  over  400  pages  on  hog-cholera,  giving  the  history,  causes, 
pathology,  types,  and  treatment.  Then,  in  addition,  you  get  complete 
chapters  on  all  other  diseases  of  swine. 


Saunders'  College  Text-Books 


l\ie>inary  Bacteriology.  By  Robert  E.  Buchanan,  Ph.  D., 
Professor  of  Bacteriology  in  the  Iowa  State  College  of  Agriculture 
and  Mechanic  Arts.  Octavo  of  516  pages,  214  illustrations 
Cloth,  S3. 00  net. 

Professor  Buchanan's  new  work  goes  minutely  into  the  consideration 
of  immunity,  opsonic  index,  reproduction,  sterilization,  antiseptics, 
biochemic  tests,  culture  media,  isolation  of  cultures,  the  manufacture 
of  the  various  toxins,  antitoxins,  tuberculins,  and  vaccines. 
B.  F.  Kaupp,  D.  V.  S.,  State  Agricultural  College,  Fort  Collins:  "  It  is 
the  best  in  print  on  the  subject.  What  pleases  me  most  is  that  it  con- 
tains all  the  late  results  of  research." 

Sii§®ini'§  AiniaitomvoiF  DomnKBiitic  Amiinniaik 


Anatomy  of  Domestic  Animals.  By  Septimus  Sisson,  S.  B.,  ^'.  S., 
Professor  of  Comparative  Anatomy.  Ohio  State  University.  Octavo 
of  930 pages,  72s  illustrations.    Cloth, $7.00  net.    New  (2d)  Edition. 

Here  is  a  work  of  the  greatest  usefulness  in  the  study  and  pursuit  of 
the  veterinary  sciences.  This  is  a  clear  and  concise  statement  of  the 
structure  of  the  principal  domesticated  animals — an  exhaustive  gross 
anatomy  of  the  horse,  ox,  pig,  and  dog,  including  the  splanchnolog}'  of 
the  sheep,  presented  in  a  form  never  before  approached  for  practical 
usefulness. 

Prof.  E.  D.  Harris,  North  Dakota  Agricultural  College:  "  It  is  the  best 
of  its  kind  in  tha  English  language.     It  is  quite  free  from  errors." 

Skairp^s  ^mtmTm^tj  Opktkalinr]i®l(0)gj 

ophthalmology  for  Veterinarians.  By  Walter  N.  Sharp,  M.  D., 
Professor  of  Ophthalmology,  Indiana  Veterinary  College.  i2mo 
of  210  pages,  illustrated.     Cloth,  $2. 00  net. 

This  new  work  covers  a  much  neglected  but  important  field  of  veter- 
inary practice.  Dr.  Sharp  has  presented  his  subject  in  a  concise,  crisp 
way,  so  that  you  can  pick  up  his  book  and  get  to  "  the  point  "  quickly. 
He  first  gives  you  the  anatomy  of  the  eye,  then  examination,  the  various 
diseases,  including  injuries,  parasites,  errors  of  refraction. 
Dr.  George  H.  Glover,  Agricultural  Experiment  Station,  Fort  Collins: 
"  It  is  the  best  book  on  the  subject  on  the  market." 


Saunders'  College  TextrBooks 


Personal  Hygie7ie.  Edited  by  Walter  L.  Pyle,  M.  D.,  Fellow 
of  the  American  Academy  of  Medicine.  i2mo  of  ^15  pages,  illus- 
trated.    Cloth,  Ji. 50  net.  ,       New  {6th)  Edition. 

Dr.  Pyle's  work  sets  forth  the  best  means  of  preventing  disease — the  best 
means  to  perfect  health.  It  tells  you  how  to  care  for  the  teeth,  skin, 
complexion,  and  hair.  It  takes  up  mouth  breathing,  catching  cold, 
care  of  the  vocal  cords,  care  of  the  eyes,  school  hygiene,  body  posture, 
ventilation,  house-cleaning,  etc.  There  are  chapters  on  food  adulter- 
ation (by  Dr.  Harvey  W.  Wiley),  domestic  hygiene,  and  home  gymnastics. 
Canadian  Teacher :  "  Such  a  complete  and  authoritative  treatise 
should  be  in  the  hands  of  every  teacher." 

OallbiriiBitk's   Ex^irckce  for    \/\f  ©maini 

Personal  Hygiefie  and  Physical  Training  for  Women  By 
Anna  M.  Galeraith,  M  D.,  Fellow  New  York  Academy  of 
Medicine.       i2mo    of  371    pages,  illustrated.       Cloth,   J2.00  net. 

Dr.  Galbraith's  book  meets  a  need  long  existing — a  need  for  a  simple 
manual  of  personal  hygiene  and  physical  training  for  women  along  sci- 
entific lines.  There  are  chapters  on  hair,  hands  and  feet,  dress,  devel- 
opment of  the  form,  and  the  attainment  of  good  carriage  by  dancing, 
walking,  running,  swimming,  rowing,  etc. 

Dr.  Harry  B.  Boice,  Trenton  State  Normal  School:  "It  is  intensely 
interesting  and  is  the  finest  work  of  the  kind  of  which  I  know." 


Exercise  in  Education  and  Medicine.  By  R.  Tait  McKenzik, 
M.  D.,  Professor  of  Physical  F.ducation,  University  of  Pennsyl- 
vania. Octavo  of  585  pages,  with  478  illustrations.  Cloth,  $4.00 
net.  New  {2d)  Edition. 

Chapters  of  special  value  in  college  work  are  those  on  exercise  by  the 
different  systems:  play-grounds,  physical  education  in  school,  college, 
and  university. 

D.  A.  Sargent,  M.  D.,  Hemenway  G3Tnnasium:  "It  should  be  in  the 
hands  of  every  physical  educator." 


Saunders'  College  Text-Books 


Normal  Histology  and  Organography.     By  Charles  Hill,  M.  D., 
i2mo  of  483  pages,  337  illustrations.     Flexible  leather,  $2.25  net. 

New  (,sd)  Edition. 

Dr.  Hill's  work  is  characterized  by  a  brevity  of  style,  yet  a  complete- 
ness of  discussion,  rarely  met  in  a  book  of  this  size.  The  entire  field 
is  covered,  beginning  with  the  preparation  of  material,  the  cell,  the 
various  tissues,  on  through  the  different  organs  and  regions,  and  end- 
ing with  fixing  and  staining  solutions. 

Dr.  E.  P.  Porterfield,  St.  Louis  University:  "  I  am  very  much  gratified 
to  find  so  handy  a  work.  It  is  so  full  and  complete  that  it  meets  all 
requirements." 


lB)@ji^mo  iL^a^EdioiriTo  jni^[Q)@r§  jriin 


Hutolosy.  By  A.  A.  Bohm,  M.  D.,  and  M.  von  Davidoff, 
M.  D.,  of  Munich.  Edited  by  G.  Carl  Huber,  M.  D.,  Professor 
of  Embryology  at  the  Wistar  Institute,  University  of  Pennsyl- 
vania. Octavoof  528  pages,  377  illustrations.  Flexible  cloth,  J3. 50 
net.  Second  Edition. 

This  work  is  conceded  to  be  the  most  complete  text-book  on  human 
histology  published.  Particularly  full  on  microscopic  technic  and 
staining,  it  is  especially  serviceable  in  the  laboratory.  Every  step  in 
technic  is  clearly  and  precisely  detailed.  It  is  a  work  you  can  depend 
upon  always. 

New  York  Medical  Journal:  "There  can  be  nothing  but  praise  for 
this  model  text-book  and  laboratory  guide." 


ii^dciifdir  §  mniintcsiiry  riiygEdinKi 

Military  Hygiene  and  Sanitation.  By  Lieut.-Col.  Frank  R. 
Keeper,  Professor  of  Military  Hygiene,  United  States  Military 
Acadamy,  West  Point.  i2mo  of  305  pages,  illustrated.  Cloth. 
$1.50  net.  Just  Ready. 

You  get  here  chapters  on  the  care  of  troops,  recruits  and  recruiting,  per- 
sonal hygiene,  physical  training,  preventable  diseases,  clothing,  equip- 
ment, water-supply,  foods  and  their  preparation,  hygiene  and  sanitation 
of  posts,  barracks,  the  troopship,  marches,  camps,  and  battlefields;  dis- 
posal of  wastes,  tropic  and  arctic  service,  venereal  diseases,  alcohol,  ttc. 


Saunders'  College  Text-Books 


Joirdaiffi^i  Gciiadiral  Bacteriology 

General  Bacteriology.  By  Edwin  O.  Jordan,  Ph.  D.,  Professor 
of.  Bacteriology,  University  of  Cfiicago.  Octavo  of  650  pages, 
illustrated.     Cloth,  $3.00  net.  New  [4th)  Edition. 

This  work  treats  fully  of  the  bacteriology  of  plants,  milk  and  milk 
products,  dairying,  agriculture,  water,  food  preservation;  of  leather 
tanning,  vinegar  making,  tobacco  curing;  of  household  administration 
and  sanitary  engineering.  A  chapter  of  prime  importance  to  all  stu- 
dents of  botany,  horticulture,  and  agriculture  is  that  on  the  bacterial 
diseases  of  plants. 

Prof.  T.  J.  Burrill,  University  of  Illinois:  "I  am  using  Jordan's  Bac- 
teriology for  class  work  and  am  convinced  that  it  is  the  best  text  in 
existence." 

Eyirci^i  Eii€ft(iri©l©gE€  Tdckiaae 

Bacteriologic  Technic.  By  J.  W.  H.  Eyre,  M.  D.,  Bacteriologist 
to  Guy's  Hospital,  London.  Octavo  of  525  pages,  illustrated. 
Cloth,  $3.00  net.  Second  Edition. 

Dr.  Eyre  gives  clearly  the  technic  for  the  bacteriologic  examination  of 
water,  sewage,  air,  soil,  milk  and  its  products,  meats,  etc.  It  is  a  work 
of  much  value  in  the  laboratory.  The  illustrations  are  practical  and 
serve  well  to  clarify  the  text.  The  book  has  been  greatly  enlarged. 
The  London  Lancet:  "  It  is  a  work  for  all  technical  students,  whether 
of  brewing,  dairying,  or  agriculture." 

BMii^  CkdmrnEcal  Aimalysni 

Qualitative  Chemical  Analysis.  By  A.  R.  Bliss,  Jr.,  Ph.  0.,  M.  D., 
Professor  of  Chemistry  and  Pharmacy,  Birmingham  Medical  Col- 
lege.    Octavo  of  250  pages.     Cloth,  $2.00  net. 

This  work  was  prepared  specially  for  laboratory  workers  in  the  fields 
of  medicine,  dentistry,  and  pharmacy.  It  gives  you  systematic  pro- 
cedures for  the  detection  and  separation  of  the  most  common  bases  and 
acids,  and  in  such  a  manner  that,  in  a  short  time,  you  will  be  enabled 
to  gain  a  good  practical  knowledge  of  the  theory  and  methods  of  quali- 
tative chemical  analysis. 


Saunders'  College  Text-Books 


L"Milk^§  ElciinffidiniiLi  ©ff  NMitoiti©!]:)! 

Elements  of  NiUrition.  By  Graham  LusK,  Ph.  D.,  Professor  of 
Physiology,  Cornell  Medical  School.  Octavo  of  402  pages,  illus 
trated.     Cloth,  ^3.00  net.  Second  Edition. 

The  clear  and  practical  presentation  of  starvation,  regulation  of  tem- 
perature, the  influence  of  protein  food,  the  specific  dynamic  action 
of  food-stuffs,  the  influence  of  fat  and  carbohydrate  ingestion  and  of 
mechanical  work  render  the  work  unusually  valuable.  It  will  prove 
extremely  helpful  to  students  of  animal  dietetics  and  of  metabolism 
generally. 

Dr.  A.  P.  Brubaker,  Jefferson  Medical  College:  "  It  is  undoubtedly  the 
best  presentation  of  the  subject  in  English.    The  work  is  indispensable." 


Physiology.  By  William  H.  Howell,  M.  D.,  Ph.  D.,  Professor 
of  Physiology,  Johns  Hopkins  University.  Octavo  of  1020  pages, 
illustrated.     Cloth,  $4.00  net.  Fijlh  Edition. 

Dr.  Howell's  work  on  human  physiology  has  been  aptly  termed  a 
"storehouse  of  physiologic  fact  and  scientific  theory."  You  will  at 
once  be  impressed  with  the  fact  that  you  are  in  touch  with  an  expe- 
rienced teacher  and  investigator. 

Prof.  G.  H.  Caldwell,  University  of  North  Dakota:  "Of  all  the  text- 
books on  physiology  which  I  have  examined,  Howell's  is  the  best." 


Bdirgciy^i  HygndEiKi 

Hygiene.     By  D.  H.  Bergey,  M.  D.,  Assistant  Professor  of  Bac- 
•  teriolbgy.  University  of  Pennsylvania.     Octavo  of  529  pages,  illus- 

trated.    Cloth,  S3.00  net.  New  (5/A)  Edition. 

Dr.  Bergey  gives  first  place  to  ventilation,  water-supply,  sewage,  indus- 
trial and  school  hygiene,  etc.  His  long  experience  in  teaching  this  sub- 
ject has  made  him  familiar  with  teaching  needs. 

J.  N.  Hurty,  M.  D.,  Indiana  University:  "  It  is  one  of  the  best  books 
with  which  I  am  acquainted." 


lO  Saunders'  College  Text-Books 


hnmediate  Care  of  the  Injured.  By  Albert  S.  Morrow,  M.  D., 
Adjunct  Professor  of  Surgery,  New  York  Polyclinic.  Octavo  of 
360  pages,  242  illustrations.     Cloth,  $2.50  net.         Second  Edilion. 

Dr.  Morrow's  book  tells  you  just  what  to  do  in  any  emergency,  and  it 
is  illustrated  in  such  a  practical  way  t.iat  the  idea  is  caught  at  once. 
There  is  no  book  better  adapted  to  first-aid  class  work. 

Health:  "Here  is  a  book  that  should  find  a  place  in  every  workshop 
and  factory  and  should  be  made  a  text-book  in  our  schools." 


American  Illustrated  Medical  Dictionary.  By  W.A.Newman 
Borland,  M.  D:,  Member  of  Committee  on  Nomenclature  and 
Classification  of  Diseases,  American  Medical  Association.  Octavo 
of  1107  pages,  with  323  illustrations,  119  in  colors.  Flexible 
leather,  $4.50  net ;  thumb  indexed,  $5.00  net.  Eighth  Edition 

If  you  want  an  unabridged  medical  dictionary,  this  is  the  one  you 
want.  It  is  down  to  the  minute;  its  definitions  are  concise,  yet  accu- 
rate and  clear;  it  is  extremely  easy  to  consult;  it  defines  all  the  newest 
terms  in  medicine  and  the  allied  subjects;  it  is  profusely  illustrated. 
John  B.  Murphy,  M.  D.,  Northwestern  University:  "It  is  unquestion- 
ably the  best  lexicon  on  medical  topics  in  the  EngHsh  language,  and 
with  all  that,  it  is  so  compact  for  ready  reference." 

Amciiriesiirii  P©€k(ift  Da€fti©iiiiiiiry 

American  Pocket  Medical  Dictionary.  Edited  by  W.  A.  New- 
man Borland,  M.  D.  6g3  pages.  Flexible  leather,  $r.oo  net; 
thumb  index,  $1.25  net.  New  (gth)  Edition. 

A  dictionary  must  be  full  enough  to  give  the  student  the  information 
he  seeks,  clearly  and  simply,  yet  it  must  not  confuse  him  with  detail. 
The  editor  has  kept  this  in  mind  in  compiling  this  Pocket  Dictionary. 

I.  V.  S.  Stanislaus,  M.  D.,  Medico-Chirurgical  College:  "We  have 
been  strongly  recommending  this  little  book  as  being  the  very  best." 

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